I do all the work on my own bikes as well as most of the work on my friend's. There's really not much you need. With a Basic socket set, screwdrivers, couple pliers and a dead blow you can do 90% of the work. That said there are 2 "Motorcycle" tools I own.
1) My overhead cam lifter.
http://www.amazon.com/dp/B000WJHAT8/?tag=atomicindus08-20
It's just a crescent shaped tool (most common) that you is used to depress the shim buckets so you can pull out the shims when the lobe is rotated opposite. On one of my motorcycle I have to do this every 2,000 miles. Each manufacture has there own style so make sure you get the right one (my Honda one is like the one above). If your bike doesn't have the shim type buckets you wont even need these. But you probably need something else.
Also for the shims (if you have them). If you're like me and have a bike with 16 valves and a maintenance check every 2,000 miles this can get expensive. What you can do though is try swapping them around with each other. Just involves some simple math and if you can prove they all remain in clearance on paper go ahead and move them around. If you need a new size though you can try exchanging a spare shim for a new one. I've heard of some shops doing this but I've called around and none around me would.
2) My Carburetor Adjuster.
http://buy1.snapon.com/catalog/item...&group_ID=1441&store=snapon-store&dir=catalog
This tool just makes it a breeze to adjust the mixture screws on the bottom of a carburetor. You can do it without one of these but its a real pita and will take you 3x as long. I prefer this type the flex shaft driver tools. You only need the tool, not the set. You can just use driver bits in a 1/4 socket (that's what I do and I have the set).
3) Shop manual / FSM. This should be self explanatory but i'll include it anyways. You really can't do anything without it. My friend learned this the hard way when he thought he could just listen to somebody else on his motorcycle's board. He ended up using the wrong procedure to time his cams and bent everyone of his exhaust valves.
Other small items that you "may" end up needing include:
Solder iron or bumper/fairing repair kit (epoxy + mesh). If your have a sportbike chances are your gonna crack the plastic at some point. Two most common fix it methods are with a soldering iron (poor man's plastic welder) or a fairing kit. I prefer using the iron but on some things they don't work (like narrow/skinny support tabs). If you end up breaking a "button" or "tab" on a fairing you can take a mold of a good one somewhere else on the fairing and solder/weld it in. If you don't have a good source you could cut up and shape some scrap plastic/fiberglass, it's ugly but it works.
An assortment of prying tools. Sportbikes have a subframe that supports the instrument panel and fairings. These subframe's are very easy to bend if you drop the bike. Sometimes it's just a simple bend and can be pryed back into position. Other times the peice is really complex and would be a nightmare (though still possible if you had the patience). In cases involving the latter I would just buy a new assembly off ebay. My favorite "prying tools" are my 28" snapon screwdriver that fell off the back of a truck (no really), 14" crescent, and jack handle.
Tire irons / Tire stand. If you race it you'll probably want these. If you wont be replacing tires often it's easier to just let the shop handle it (some will do it free if you buy the tires from them). Personally I think removing a tire is the biggest PITA I could imagine so I just let the shops do it. Balancing is pretty simple but I don't think it has a large effect (I've heard some mechanics say you don't even need to do it). But simple to do (or free) so why not?