Originally Posted by AndrewP
The best value in tools are the sets for about $40 from Performance or Nashbar. It will include several tools you never use, but will include half a dozen tools that will cost from $5 to $15 at the LBS, that you will be sure to use. The rust on the cogs wont do any harm, so clean an lubricate sparingly.
While you're at Home Depot get yourself a set of metric allen wrenches. Don't be afraid to spend a little more to get good ones. You'll be surprised at how much bike work you can do with just them.