Alpine units are very nice, and pretty easy to use. You need an Ai-net unit, which I believe start at around $200, to be able to use an auxillary input adapter, which is an extra $15. Panasonic units are also very nice, and most of them have an aux input. The JVC Digifine units, although retail priced around $400, are awesome units... there is a good possibility to find them on special, possibly at crutchfield, they have both front and rear aux inputs... however, the brushed aluminum faceplate has a hard time fitting in with most car interiors.

If you need more help deciding, give crutchfield a call... tell them what you want to spend, and what you're looking for... if you're not exactly sure what you want or what something is, they will explain things pretty well. If you order from them, they'll also include a free dash kit and wirring harness.