I recomend that you buy the Digitech RP80. It has 40 preset and 40 user made efects. It simulates other amp models. And you can get just about any sound out of it with careful programing and it has a very easy to understand manual. It only costs around $70 so not to break the bank. It also has built in effects and tunner and drum machine to practice with. Unlimited things it can do.
If you want something a bit better then look into the Digitech GNX series.
Hope That Helps