I know that Crutchfield has modules/harnesses that allow the use of steering wheel controls on some vehicles. You might want to check out what is available for your situation.

I like the suggested Pioneer. Kenwood has a nice unit, too. Modern GPS, bluetooth and good radio functions, that is all good.

I have a portable Garmin on a beanbag stand for my X, working through an auxiliary port. It has bluetooth, MP3 player and of course the GPS function. It is not nice and integrated in looks, but the steering wheel controls work and it functions perfectly. I upgraded the BMW GPS software and all that, but it still isn't satisfactory for me. Even a modest modern aftermart GPS is better.