Given your price range and the fact you own a two seater, it seems you're looking for something sporty. I'd suggest:
Infiniti G35 or G37. The former can easily be gotten completely loaded for under $35k (and possibly out the door if you pay cash and go for an unsold 2008 model). The latter can be a little pricier, but not by much.
I've got a 2007 G35 Coupe. Fully-loaded (except for four wheel steering), stickshift. Intense amount of fun to drive.
Prior to that I've had a 2006 G35 Sedan (was rear-ended on US-101 and the car was totaled; which is why I couldn't wait for the G37 to come out, I needed something I could drive soon).
Simply put, this is the most fun with four seats (and the lack of insurance premium due to being a "sports car") you'll have for under $40,000. Rear-wheel drive (AWD available on the sedan), real stickshift available (unlike on the IS350), sporty suspension, limited slip differential (the BMW 335 - which is $10,000 more expensive doesn't include that).
The big downside is fuel mileage (if I stay in fifth and sixth as possible as possible I can get a little over 26mpg, which is still dismal). This is slightly better in the newer models, but still - if you're looking for a fuel efficient car this isn't it. It also requires 91 octane (older models could take 89 and below if with an automatic, but that's not recommended).
Other downside is small trunk space on the 2007 coupe (the sedan is much better; not sure about the 2008 g37 coupe).
Also buy used, unless you're looking to build credit - which may not be the best time for it. When I got my first G35 (the sedan), I a) could get a certified deposit for a rate that is higher than what I am paying for the car b) was less than a year out of college, with no credit history.