Well I know you said floorstander, but $200-$300 will give you some nicer options if you go for bookshelf speakers. If you know you're always going to be running with a sub, then you should be fine with a pair of good bookshelf speakers up front.
What is your current serup for receiver / speakers? Is the receiver one that was included in that $99 for a 5.1 system. I'd be rather worried if it was
For some suggestions to look at for bookshelf speakers:
AV123 x-series
SVS SBS-01
Axiom M3v2
Ascend 170
Those are getting to be a bit higher than you were looking, but going used is another great way to save some money if you're willing to do that.
Without knowing what kind of sound you like though, it would be pretty tough to try to pick something out online.
Going in to some retail stores and listening to some different options might give you an idea of what kind of sound you like.
Paradigm, Klipsch, Boston Acoustics, Monitor Audio, and a few others should have bookshelf speakers in this range.
As for floorstanders, it would be tough to find a set of floorstanders from brands like these. You might be able to find something from Polk (I know they sell R30s for $50/each, which is way under budget for you), Infinity (Primus line), JBL (Northridge series), etc.