Decorations

The most fun thing about having dreads is the ability to easily decorate them. You can do so with bead, yard wraps, sleeves, sewing things into them.. the list goes on.
Beads

(Above: Various wooden and plastic beads not intended to be worn in dreads but can be used as such)

(Above: Various home-made beads. Dark ones are ceramic, light one is carved from a piece of a deer's antler)

 Beads are the easiest to come by. If you have small dreads (pencil width or smaller) then you want beads with a small hole, and the reverse goes for big dreads. You can find beads at craft stores (yes, even ones with huge holes for average-huge dreads) or you can make them. Materials they can be made out of are: glass, wood, bone, antler, plastic, clay, porcelain, and even metal if you have the means of doing so. Glossy beads tend to slip off if they're not snugly on the dread. If you don't glaze clay dreads, or use stain instead of glaze then they turn out a bit more rough and will hold on better with the friction.
Metal Hardware

(Above: Poor quality picture of a hexagonal nut and an un-threaded metal washer-thing that I haven't discovered the purpose of)

There's also things you can use that are similar in weight and size to beads but aren't used for that purpose. The most common is metal hardware.
This includes nuts, washers, and anything else you can find on the street or at a hardware store. Rusty metal hardware will spread the rust into your hair and thus turn that section of hair green or brown. This doesn't really harm your hair unless the exposure to it is prolonged. Stick to stainless steal to avoid problems
You can also use bones. The best type of bone to use is a vertebrae. Cats, possums and other small mammals have vertebrae with a pencil sized hole. Dogs have larger vertebrae with a hole you could fit your finger through. Anything bigger and it will just be too much weight and too pointy. You can find bones frequently on the railroad tracks, out in the woods or on the beach. Clean them off with soap and warm water, remove any organic material. You can use hydrogen peroxide to clean them if you want. Just don't use bleach. It makes them very white, but it makes the brittle as well. You can clear coat them to strengthen the bones with a mixture of Elmers glue and water (ratio of glue to water is 1-5 or so). I can post more on bone preservation upon request.

(Above: This picture features 2 vertebrae and a pelvis from a pug dog and 1 vertebrae from a possum. I don't condone killing animals for their bones, that's just pathetic. Find an animal that is already dead and remove the organic matter, or just use bones that you find already stripped.)
Yarn-Wraps

(Above: Animal-dread wrapped in black and red yarn. Originally it was all one solid wrap but it got warped over time and now has open gaps that show dread.)

(Above: Yarn used to conceal connection point between my dread and an animal-dread. Black yarn with white yarn making a cross-hatch design over)

Yarn wraps are pretty sweet. You can make them last for a few weeks or make them permanent until their desired removal. You can use any yarn, and can have more than one color per dread if you want. To make them temporary then tie the yarn around the dread and start wrapping from there. To make them last longer use a big sewing needle with a big hole to sew the thread through the dread, then tie it and begin wrapping. You can make thick beatlejuice looking stripes by tying two or more different colors on, holding all but one against the dread and wrap the one you separated around that dread and the yarn being held against the dread. Then once the stripe is as long as you want it, put the separated strand of yarn against the dread and pick a different color to replace it and make the next color stripe. If you want a pattern of yarn-dread-yarn-dread then make a stripe as described, then for the dread stripe simply use the big sewing needle to insert the yarn through the dread, hiding it within the dread until you want the start the next yarn stripe. You can also make stripes that are 1 strand of yarn thick, by just taking 2 colors of yarn and wrapping them both around the dread together. OR, you could make super crazy ass patterns by constantly switching up the yarns and making it chaotic. There are lots of possibilities with yarn.
One thing to watch out for with yarn is smell. It takes a while for them to mold, but they will start to smell like they are if you get them wet too often. This is because they hold in moisture, both in the yarn and thus in the dread as well. Be sure to wring them out well after rinsing them, use a towel, even blow-dry if you have to.
Another thing to be weary of with yarn. This is something I found out entirely on my own. If your dreads are young and not fully dreaded then I don't recommend you get yarn-wraps just yet. They can at times force the dread to become lumpy and uneven due to the yarn basically constricting the dread. Also if the dreads are rather new and not locked up then the dread may involuntarily weave the yarn into it. This makes the yarn really hard to remove and you may end up with chunks of it permanently stuck in there. Yarn-wraps do in a sense make dreads tighter, but they have to already be pretty well dreaded for this to happen.
Wire Wraps:

Much like yarn, wire can be used to wrap dreads for decoration. You have use stainless steel wire otherwise it will rust. The wire I used is Stainless Steel Lockwire, commonly used in electronics and construction. It can be found at most hardware stores. The tricky thing about wire-wrapping is doing it in such a way that it won't poke you. I solved this problem by shoving the ends of the wire into the dread so they're surrounded by a cushion of dread. You can wrap the wire in any style you want. It's best not to make the wrap more then a couple inches long, because where you wrap it will be stiff, obviously, and you don't want your whole dread to be like that. Wire wraps look pretty cool, especially if you're going for that steam/cyber punk look.
Sleeves

(Above: Two sleeves, one made of many pieces of black and brown leather, the other made of a single piece of black leather. All sewn with dental floss)

Sleeves should only really be made of leather. To make a leather sleeve take a piece of leather roughly 8" long by 2-3" wide and sew it up hotdog-style. This makes a leather tube. The hard part is getting it on. If it is too wide then it will never stay on, so you want it to be snug. You'll notice how hard it is to get on since you can't reach the tip of your dread through the other end to pull it through. There's 2 ways to get the leather wrap on, both ways I invented. One way is to use yarn and the big sewing needle. Tie one end of the yard through the tip of your dread. Make sure it's on there well. Take the free end of the yarn and put it through the leather sleeve. Then just line up the sleeve to be pulled on and pull it up while pulling down on the yarn. If the yarn breaks off then you didn't tie it on well enough. Another way is to kindof inch your dread through the sleeve. Put the tip of your dread through the end of the sleeve. Now just work the dread slowly down through the sleeve. Scrunch the sleeve up the dread, pinch the tip of the dread on a further down point of the sleeve, and pull the top of the sleeve further up the dread. Do this until the tip of the dread finally pokes out the end of the sleeve to where you can just pull it through.
Some people sew the leather sleeves right onto their dreads. This way you don't have to worry about getting the dread through it. This does, however, mean that it is permanent until you remove it, and it will trap in moisture and potentially mold. I've done this and as long as you keep it dry and don't sweat on it then you'll be fine.
Patches
There's also the aspect of sewing patches, hemp-work, and other fabric-type knick-knacks to your dreads. No real rules on how to do that, you can do it however you want. I would typically take a long piece of interesting looking fabric and spiral it down the dread, sewing it on with dental floss. This looks pretty cool. I sewed a zipper to my hair once (the teeth part, not the puller) and that looked pretty sweet as well.