'05 GT Mustang is the obvious answer. Here are some pluses and minuses of some of the other vehicles though...
The Titan looks nice, if you like absurdly huge pickups. If you want to go the pickup route, though, I would go with a single cab HEMI Dodge Ram - about the same price range as the Titan, maybe cheaper - looks better and sounds way better too.
V6 Altimas are pretty quick and probably more roomy than the Mustang but if you're interested in buying a Mustang you're already willing to sacrifice a little space for more power and better looks. If you plan on getting married and popping out kids in the near future though this is a good choice. The slightly different look for '05 on these is an improvement.
Accords you could pretty much say the same things about as the Altimas - both reliable, both sporty leaning towards "dad wanted sports car, wife wanted full size sedan, and they sort of met in the middle."
Scion tC is the first Scion designed for sale in the US that wasn't a shoebox (xB) or a doorstop (xA) already driven in Europe and designed to cram into tiny parking spaces. For a FWD, for its power, and for its price, it should be a top choice for ricers but Toyota has that reputation for bland but reliable. I don't like its tail end - it doesn't fit with the rest of the car. The interior is not at all bland and the roof (all glass, I think) is pretty cool. Not for me, but cool.
Anyway, I still say '05 GT is the best choice - and this coming from a guy who said he'd never buy a (new) American car again (nothing unpatriotic meant, I've just had horrible experiences with Chrysler/Jeep and GM). This is the best (affordable) sports car I think Ford or anyone else has made in decades.