Superlux E100

Dirt cheap but really well built and weighty. Great for getting a metal-style 'clicky' attack on kick drum, though I wouldn't want to use it without something on the outside to pick up the lower frequencies. It works for typical boundary mic stuff too (on a table in meetings). I've not really tried it on any other instruments though.

Only slight annoyance is the built in cable - I assume it's because the mic is so small a regular XLR socket wouldn't fit, but cable fitted to it is pretty flimsy.