Chris:
Based upon my experience and that of some friends here in Texas and Louisiana, almost any motorcycle can be made street legal by the dealer. They can title it as a DS bike instead of an "off road only" bike. I would negotiate based upon them getting it street legal, if you are going new.
As far as bikes go, IMHO there is no bike that stands up to the Honda XR650R. I have personally ridden my XR over 4,000 miles since I got it a bit over a year ago. I have a friend that swears he has put 30,000 miles on his. It is everything that I could have ever wanted. Honda has dropped the XR-R from their lineup in OZ, and will likely do so in America eventually, but until they do (or they redesign everything except the mill) the XR-R is top dog in my book.
That being said, I can't imagine riding it on single track, but you could likely dig a moat from the Atlantic to the Gulf of Mexico with the right tire.
Husky has been getting good press, but I know very little about them. Enduro_Nut ran one for a while.
I have a KTM 400 and love the bike. That being said, the RFS bikes are more labor intensive than my XR-R. They are much better suited for tight conditions.
I know a bunch of guys that swear by the Kawasaki 400 and four or five that have made the Yamaha WR450 into a DS bike. In Texas that is easy, but I don't know about the laws in Florida. There is a bunch here that rides the KLR 650, but it is not a "dirt bike" in my book.
One way people seem to be getting around the law is buying a bike that had already been converted in another state ...
Hope that helps!