350 is a very small budget to be honest... Brand new, a
B-stock EMP Tek e5ti can extend down to ~60hz and fits the bill for clean bass, excellent midrange / voice intelligibility, and a clean, smooth treble. EVen then, though, i
still recommend pairing with a subwoofer to get
full extension. Another one to consider is the
Infinity P363. A pity the Speaker Company (Boston Acoustics' ID Brand IIRC) doesn't make stuff anymore. Getting a bit more expensive, there's
this. Go to your local big box retailer and ask to listen to some Klipsch RF-52s and some yamaha 310s too and see if they fit what you're looking for.
Really though, strongly recommend a separate subwoofer, as placement can affect bass quality. For example if you went with a pair of Behringer 2030p's and paired them with a cheap sub (maybe a lavasub 10 inch), you'd get a nice starter system.
My real recommendation though would be to scour the classifieds and try to find something used up for sale. It can be tough looking online though, since no one ever wants to ship =\
http://forums.audioholics.com/forums/showthread.php?t=69370
http://www.audiogon.com/cgi-bin/cls.pl?spkrfull&1291927718&/Psb-Image-T55-floor-standing-t
http://www.audiogon.com/cgi-bin/cls.pl?spkrfull&1291643444&/Paradigm-Studio-80's-price-red
http://www.audiogon.com/cgi-bin/cls.pl?spkrmoni&1293468917&/Infinity-Cascade-Model-Five-ba
Craigslist / kijiji are a better place to look locally. That's my ultimate suggestion.