I had the OEM headunit with my 2 12" JL Audio 12W3's and the system kept spiking, my audio shop said I had to buy the JL Audio Clean Sweep which is a module that balances out the levels so that you get a nice, even sound. However, the price is enough for me just to buy a new headunit. It doesn't seem worth the price to retain the OEM headunit, so I opted to buy a Panasonic CQ-VD7001U on eBay for 518 and so far I'm happy with it. It's touchscreen, indash dvd, cd, and has inputs for NAV, Backup Camera, and video game console.
If you are willing to spend the extra money, I suggest the Alpine IVA-D310 or the Alpine IVA-W200 which is a double-din headunit. Alpine has the best products. Also, Pioneer AVIC lines are nice, the AVIC-N3 has just been released, and so far I've heard its an amazing product. It comes with NAV. The Alpines require purchase of the NAV module unit.