I use a pretty standard scanner to scan fanart and a graphics pen and tablet to colour. (Basically graphics pad and pen act as a mouse, but is generally much faster and easier to draw with on computer) Mine is a Aiptek "Hyper Pen", with pressure sensitivity. I've never used any others, but mine seems to be pretty good, especially for drawing detailed backgrounds on computer.
It does, of course, help if you have a reasonably fast computer, especially if you're going to use programs like Paintshop Pro or Photoshop Editor. I manage on a Pentium II, but I wouldn't want to try colouring a six+ layer image on anything slower...
The last (pretty obvious) thing is screen resolution. If your screen can support it, then it's best to keep it set to at least 16-bit colour. It's also wise to remember that different computers will display images differently.
