I added a kit like this to my 2005 Silverado and it worked well. In that rig, the stock stereo was integrated into the electronics and it was a pain to change out so the kit was a lifesaver.
All my other cars, I've replaced the stock HU as soon as I could.
I just put this in my wife's 2006 CR-V: http://www.amazon.com/gp/product/B00...ls_o06_s00_i00
Only $75 and it does full iPod control as well as have an Aux in. She doesn't care that much about high fidelity but it sounds pretty good anyway. To be honest, that car is so noisy that spending more than a $100 is a waste.