I will highly recommend Pioneer FH-P8000BT as head unit.
I got one from Amazon for $250 shipped and no tax.
I did not want NAV or DVD unit because I already have top end GARMIN GPS and I drive this car mostly alone and do not need DVD playback feature.
Price/features that headunit is hard to beat.
1. Seamless integration of hand free calling thru built in Bluetooth, also you can transfer your phone address book contacts, so you will see who is calling you and make calls FROM your Headunit without even touching your phone. I have it installed in my car for almost 4 month and It is working perfectly with my old Treo650.
Bluetooth can be also used to stream music from your BT enabled phones or MP3 players.
2. Full Ipod controls. My 80Gb Classic is in my glovebox all the time. I can control EVERYTHING directly from Headunit. Pioneer is using USB port for controls so it also charging Ipod.
If you do not have Ipod you can connect USB thumb drive or even external portable hard drive (you can get one pretty cheap) and listen to all your MP3s.
3. Very few buttons, so it is very easy to navigate.
4. Of course it have all the basic features as CD, AM/FM, EQ, etc.
You can also add XM, Sirius, HD Radio.
CUBE