The trimmer I've been using for capacitors and coils lately is a nylon tool with a metal bit that I got from Hamtronics for $3: it's "A2 tuning tool" at http://www.hamtronics.com/accys.htm#tools - it's actually a Sprague-Goodman GTT-5G. I'm sure I should be lusting after some sexy ceramic trimmers or something, but this does the job just fine, and the price is right.