I am looking into getting an 4.4i or 4.8is X5. What the differences in the 03 through 06 models?

This may help a little....

http://www.x5world.com/articles/x5/general-information/31660-how-tell-options-you-have-your-x5-all-e53-years.html

consumerguide.com has great model year comparisons.

click on automotive, then used, then bmw and find the x5.

04 and newer are the ones to have. upgraded styling, xdrive, and panoramic sunroof with certain options adaptive headlights, etc.

in 05 they added bluetooth std

good luck