If you're concerned about OEM appearance you will have to make some sacrifices, just about any aftermarket head unit will give you better features, and better sound quality, but you lose the OEM aesthetic. If you want to go aftermarket, Kenwood and Pioneer have some great head units, Kenwoods play a little bit better than the Pioneers with regard to integration (specifically the navigation), but both will integrate well using the idatalink maestro.
Really anything is better than the one you have though, it distorts badly from one click to the next on the volume knob (I can't remember exactly where without checking). If your goals are high level of sound quality, go aftermarket, but you just want to improve what you have and keep on OEM look, then there are a couple of plug and play OEM replacements that you can choose from.