I don't really know your budget. I've owned several
brands in this size range over the years. If you can
find a set of Pioneer TS-T5s that would be my very
first choice. They are really OLDSCHOOL and I mean
OLD, but they are fantastic drivers. My second choice
would be a VIFA, its a very smooth sounding driver
not harsh, very accurate
http://www.madisound.com/catalog/product_info.php?products_id=1088
NEXT choice would be the MBQuart. I've run those
in two different cars. I wouldn't run a lot of power
to them, they are pretty efficient but can be harsh
if you run a bunch of power to them.
You can find a bunch of really nice drivers form
PartsExpess to fit your needs. All of us can suggest
brands and such but your going to be limited mostly
by depth. Even so, if your vents get in the way you
can heat them up then push the driver down to gain
a bit of room.
http://www.parts-express.com/wizards/searchResults.cfm?srchExt=CAT&srchCat=576