Step 2: The Dremel's Bits
Fiberglass Cutting Disc - I love these guys, they are the largest cutting bit you can get for a Dremel, and they tend to last for a good while before breaking. Advantages include deeper cuts and they're able to cut stronger material, such as metal and ceramic. Disadvantages are that refill packs are about $10 for five of them.
Standard Cutting Disc - Also decent for metal, most replacement packs come with many for cheap. They break often, and I've been nicked by flying disc-shrapnel before. Used for all-purpose cutting. Use these before your nice fiberglass ones.
Carbide and Standard Grinding Bits - Both essentially the same, the carbide bits are designed more for metal, however the standard ones work well on it too. Use these whenever you have to take down sharp edges on something. The small carbide one is decent for drilling holes through metal, just make sure you center punch it with a nail or something beforehand.
Various Sized Sanding Bits - Almost self explanatory, use these for sanding wood inner corners and edges. Note that these will break very quickly if you attempt to use them on metal. The sanding discs are used primarily for flat surfaces and edges, you could call these disposable, refill kits are cheap and plentiful. More information on how to change and replace these later.
Carbon Steel Brush Bit - I love this one as well. Very useful for cleaning out tools and taking paint off anything. Scrapes away delicately on a lower setting and more vigorously on a higher setting. Can be used in place of a larger wire brush wheel to clean files.
Drill Bit - When I don't want to go out back to my drill press or get the DeWalt, this is a worthy substitute. Whenever drilling into anything, be sure to center punch it with an awl or Leatherman tool.
Brush Bit - Not truly a drilling bit, but still worthy of mention. Can be used for....well for brushing things. Not the most useful attachment, but it's handy to have...sometimes.