I said it above, but not very clearly...
I use the Zoom G2.1u effects pedal. It cost me about 75 quid, so it's not breaking the bank, but I am most impressed with the quality of output it gives. I'm not the biggest fan of modelling - I don't care what the sound is "meant" to sound like, only what it really *does* sound like! This pedal also will run off a USB cord (without the power adapter, if you choose) and acts as an audio card in Win2k/XP (not tried Vista), which makes it very very easy to record direct, listen through 'phones, etc etc.
I use it in the studio, too - I just prefer the huge range of flexibility it gives me with the 'solid state' amp I have (Randall RG200 G3).
BUT, having said all of that, the most important thing is to try a few options out in a music shop with YOUR gear - see what really works for you!
Hope this helps,
Roo