To repeat: "Stuff Zoom". That is, do not buy anything that has the brand name "Zoom" on it. There is a reason that Zoom products are so cheap.

Instead, check out the Boss GT series (GT-3, GT-5 & GT-6), the Boss ME series (ME-50 is really nice, and affordable), Yamaha DG Stomp, Digitech RP series, or the POD.

Remember, you get what you pay for. Pony up a hundred or so extra bucks and get something that you won't bin after 2 months.

The difference between amp modellers and multi-effects are apparent from their names. An amp modeller is a unit that mimics famous amps (e.g. Mesa Boogie, Marshall, Fender Blackface, Peavey 5150, etc.). A multi-effects unit is a box that can produce several different guitar effects (e.g. distortion, delay, chorus, flanger, wah, tremolo, etc.). Personally, I don't see much use to amp modellers, but that's just me. Some other people couldn't give two hoots about flanger, but they need to have that ol' Silverface sound.