Well, a Korg Kaoss Pad is very versatile and is a very good sampler. I know you only have access to four samples at a time, but it lets you load a bunch through a USB connection and an SD card, so you should have access to more.
http://www.korg.com/gear/info.asp?A_PROD_NO=KP3
Any case, these are the cheapest samplers I know of with the newest, shiniest Kaoss Pad retailing for $400 (you should be able to talk them down to $325). There are a few other models, including a mini, which are all cheaper and they should all be good samplers.