i wouldn't get a used one though. especially if it's a hard drive ipod and not flash based. that said...unless you really want the space of a classic, i'd recommend the nano or touch. flash drives ftw.
my roommate uses his suffle for riding and loves it. i went with the 4 gig nano just b/c i wanted to have a screen to be able to specifically choose what i want to listen to. i'd recommend going with a refurb, same warrenty as new, cheaper price. it's how i've bought almost all my apple gear. The Apple Store (U.S.)
i've got an 8gb touch and its sooooo fun. the thing is surprisingly tough. i've dropped it a dozen times and its got quite a few battle scars but if you get a screen cover it'll be fine. as thin as it is this thing is a TANK!
that being said it's quite a nice piece of hardware. the touch screen is really nice. its a totally new concept where you get to touch what you see and make it bigger and smaller. i took it with me snowboarding and let it chill out in my pocket while i listened to it. the thing was just fine. not a scratch on it :]
i have a 30GB video ipod and i love that thing, use it constantly and it has never had a problem. the only thing about taking it boarding tho, it doesn't stand up to the cold very well. when it gets cold the battery acts like it's dead, but once you warm it back up it's still charged.