You can use the SB gear calculator to figure out what kind of cassette you might want to go with. I use an 11-28 and am happy with it, but your mileage may vary.
http://www.sheldonbrown.com/gears/

As for the type of cassette and what you get for each step up, it really all boils down to the type of finish, how the cogs are stamped, how they're held together, weight, etc. Sometimes the cogs are coated in chrome plating rather than nickel or silver to prevent corrosion. For your money I think you'll be happy with an HG70, which can be found for 35 bucks at most bike shops, but then again your preference may be different from mine (I'm a Shimano guy, myself).

Hope this helps.