I just want to buy some cheap 6.5" speakers for the rear and need to know if they just drop right in or do I need some type of adapter kit to make them fit? Anyone know for sure?

You will need an adapter.

http://cgi.ebay.com/ebaymotors/6-5-Speaker-Adapter-Toyota-07-08-Yaris-Scion-08-xD-xB_W0QQcmdZViewItemQQcategoryZ38646QQihZ023QQitemZ360043725704QQrdZ1QQsspagenameZWDVW

i was able to install 6.5" polks in the rear with the brackets they provided.

Thanks guys... I ended up buying the adapters anyways and picked up a pair of Pioneer coaxials.

randomsuper - how much for the head unit?

I highly recommend the Ebay speaker adapters posted in this thread. I just got done installing my rear speakers and these adapters definitely made it look like a A+ professional job... Well worth it IMO...

Thanks again for the link detroitbassxb.