The cheapest good multiFX pedal IMO is the Korg AX3G at $50. Going up from there is a good selection of FX including anything Korg Toneworks AX1500 or AX3000 in the $200+ range. I good things about the new Digitech RP150,250,350 series.
I recently picked up a Digitech GNX2 for $75 off Craigslist. I've seen them go for around $100 with s&h on eBay. I highly recommend this unit at the $100 mark. This one's cheap and going in 3 hours....
GNX2 GeNetX Guitar Processor - (item 280137468288 end time Jul-30-07 10:18:45 PDT)
and another one right after it...
DIGITECH GNX2 GENETX Guitar Processor - (item 130137113537 end time Jul-30-07 16:00:50 PDT)