I have a Behringer mixer that is cheap and does a great job of getting your signals up to snuff for feeding into the computer. This is the cheapest at $50...
http://www.musiciansfriend.com/produ...ers?sku=631238
I recommend spending the extra $10 and getting the 1002. It has a line in/out feature that makes it a bit more versatile.
http://www.musiciansfriend.com/produ...ers?sku=631237
The one I have is the 1002FX model and has the ability to add some effects like reverb into the mix. The FX is handy for the extra $20.
http://www.musiciansfriend.com/product?sku=631256
Finally if you wanna stay cheap and get 4 low level inputs then consider....
http://www.musiciansfriend.com/produ...ers?sku=631236
The small price differences and the added features can nickle and dime you up, but that the fun of buying cool stuff cheap
.