From there, you might make a list of the sounds you're looking for, and what box(es) will make those sounds. If possible, listen to some different pedals at your local music store, or ones owned by people you know. Best of all would be hearing one on your own guitar/amp setup, or one very close to yours.
I've found that if you read the reviews at Harmony Central or similar sites, there are very few pedals that don't have a few "It sucks!" comments mixed in with the "I love this thing!" reviews. A high overall rating (8.0 or better) and a great eBay deal might help your decision. :cool:
Also be aware that a given effect may sound different once combined with others, even one other, and it may depend on their order in your signal chain. ("Hmm, do I want fuzzed wah or wahed fuzz?")
One final link, to a thread on Expert Forum about multi-effect pedals. Read what "Musicalhair" has to say about pedals in general and multi-effects in particular:
http://www.musicplayer.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=19;t=011200;p=1
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Doug C.