A few years ago, I wrote about cheap wooden discs as D&D minis, and I've been using them ever since. They do a great job, and cost nearly nothing. For the most part, we've used a few for the PCs, marked with the characters' initials, and the rest for NPCs and enemies, usually marked with numbers.
With D&D 4E, we've tended to have combats with more and more varied enemies. (Minions are wonderful things.) Numbering has become insufficient. It's too hard to remember what numbers are what monster, and to keep initiative order separate from token numbers. In the past, I've colored a few tokens in with the red or green whiteboard markers, and that has been useful. So, this afternoon I found my old paints and painted six sets of five colors. (The black ones I'd already made with sharpies.)
I'm not sure what I'll want next: either I'll want five more of each color or I'll want five more colors. More colors will require that I pick up some white paint, while more of those colors will only require that I re-match the secondary colors when mixing. I think I'll wait to see which I end up wanting during real combats.
These colored tokens should work together well with my previous post about using a whiteboard for combat overview. Like-type monsters will get one color, and will all get grouped to one slot on initiative. Last night, for example, the two halfling warriors were red and acted in the same initiative slot. The three halfling minions were unpainted, and acted in another, later slot. Only PCs get their own initiative.
I think that it did a good amount to speed up combat, and that's even when I totally forgot to bring the combat whiteboard (and the character sheets!) with me. Next time, we'll see how it works when it's all brought together.