Anybody who can help me identify this, if it is a 2005 or a 2006 caad 8? Can you give me a little more information on this caad 8? Specially the fork!

If you're sure it's from 2005 or 2006, I'd say you have 3 possibilities:

Most likely (based on looks, and stem) https://www.cannondale.com/bikes/06/C...del-6RR9D.html
Second, based on color: https://www.cannondale.com/bikes/06/C...del-6RR8D.html
And final, based on looks https://www.cannondale.com/bikes/05/c...del-5RR1D.html

Specific component list on those pages, and the 2006's list Fire stems (05 not), but neither fork is called "aero" so could be a swap. Just my thoughts...

Any other stock parts you can list would help narrow it down easily. ie, if that FD is stock, what is it? same with seatpost. Actually all three listed above have different front derailleurs. That could well answer it.

If you have the serial number you can tell the year based on the info at this page:

https://vintagecannondale.com/info.html

Thank you for the response! Seller says it came with 105 STI 9sp shifters, ultegra rear derailure, truvativ crank, shimano 550 wheels. Say's it's either a 2005 or a 2006, brand new. Can you give me an idea how much would the frame, fork and headset would be worth now?

300 - 400 maybe....

None of the links I provided have a bike with 9 speed. They are all 10. Also, the only bikes that had the Slice Aero fork (that I can see) are the Tri bikes, which that is most certainly not.

300-400 seems a touch conservative to me, but yeah, if you can get it for 300 and it's solid, I say jump on it.

Good luck.

its the tri model with the slice fork. exact same geometry as others it just has the strait blade aero fork