Ive built my toolbox up over time, most of it is bike specific stuff and the rest is usefull junk, If you wanna get started you cant go wrong with Wiggle for tools Ive found.
Park are the best, but pricey, I would say they are worth it if you work on bikes all day every day but most of the tools I have are Lifeline or Icetoolz from wiggle.
Heres a pic of the main tools I have.
1. Hex key set, I would say get these before you buy anything, they are a god send. Mine are Lifeline from wiggle and they come with a wall bracket but i binned that.
2. Shockpump.
3. Park tools hollowtech bottom bracket tool.
4. Icetoolz Peddal spanner. I always suffered with a massive adjustable so I got one of these to ease things. Much better.
5.Chain whip. If you wanna pull the sprocket off you will need one!
6. Cassette lock ring tool. If you wanna put your cassette back on you will need one of these. You can get a smaller version with a nut on the end you se a large adjustable spanner with.
7. Philips screw driver, Cheap enough to buy, I still need to buy a flat head one.
8. Chain splitting tool. I dont use this as much now as I have a super link, however i am thinking of getting a newer better one at some point. Lifeline do a good one with a nice big handle.
9. 8mm Spanner. This is the boy that fits everything on HOPE brakes, Bleed nipples and the hose connectors at the levers.
10. PARK torx key set. These will be a must in your toolbox too, a lot of hex bolts are being replaced with these, they dont round off as easy. I use mine for the chainring bolts and the caps on the HOPE brake resivoir caps.
11. Pliers, I still need to get a set of thin long nosed pliers.
12. Cable cutters. Another very handy tool. I got these coz i Messed up a gear outer by trying to cut it with my pliers, well worth getting if you want the job doing properly.
Like i say, I have other bits and bobs in my tool box but they are the main and im still adding slowly. Some good grease is also good to have in your box.
Another bit of kit that I have is a workstand. Expensive i know. I got mine, the Spin doctor team stand off wiggle, at the mo they are about £80 but i got mine for half that, Keep an eye on there because now and again they offer them cheap. Its not until you use one that you find hoe handy they are, I even wash my bike on mine!