$300 is a tough budget, I am guessing we are talking about something for music only that could stand alone with out a sub? thats tough... I am crazy about bookshelfs, I like them all, lol...
That being said.. With a $300 msrp I think the winner for me would be the Wharfedale Diamond 10.0, its a small driver but the speaker sounds good, next down the line would be the wave crests for under $250 its a nice set of books for sure... There are a bunch of honorable mentions, most already mentioned here, but to add one the audioengine p4's sound good to me, not as good as the hvl's for the money but I nice little speaker...
Now if you just go up $100 the world opens up...
Epos epic 2's
EPOS EPIC 2 BOOKSHELF SPEAKERS (PR) at Music Direct and Carnegie csb1's to name a couple I have bought in that last year... Both audiophile build quality and sound excellent...
So many speakers stored in my brain, I can't remember what they sounded like but I remember my thoughts and impressions when I listened to them, certain speakers stand out. PSB imagine T2 towers, actually the entire imagine line impresses me, PSB is what it is, but them speakers are all worth a listen, they cost what they should, but sound very good, the imagine mini's kick ass for their size, Ascend sierra towers {I don't see the point in spending more than they cost since I heard nothing that can really blow them away}... HSU uls15 dual drive {insane bass quality, again, no need to spend a dollar more}, I can't really think of anything that stands out for under $300, sure stuff sounds good, the nht's for instance, a great little speaker, did it surprise me? No, maybe because I heard so much about them I expected more, even the wave ccrests, they sound awesome for the price, you get a lot for your money, but nothing that would stop me in my tracks, is there a better speaker for less money? Probably not, but if you step up to $400 you get a lot more, if you step up to $900 there are a couple others that pop into mind Philharmonitors, Sierra 1's both of which I would but side by side with the csb1's and give them the edge over the epics, then you go to $1500 and you take another step up in my opinion the last step before you really have to spend a lot of money to get better sound, the Kef 50's, the ascend sierra 2's {winner}, jades, and a few others that hang on by a string and cost more...
So getting the most for your money should be key with speakers under what I call the "I just want to spend money" Budget, the sound should appeal to you and not offend your senses, in other words easy to listen to the highs and lows will be the weak points, the mids should be nice and livable hence the 10.1's and the HVL's, you pay a little more and you can get some nice highs with the good mids {csb1's and epic2's}, spend a little more and you will get better highs, and a little stronger low end {harmonitors and sierra1's} with the nicer mids, then spend doubel thta and get the sierra 2's which have great highs and mids, and can hold their own on the bottom with out a sub {I would have a sub with them}, after that IMO you are spending just to spend, you either want a different name, look, or a more pronounced sound somewhere, like you are looking for a specific sound..
BUT anyway, I don't know why I am rambling today, my vote goes for diamond 10.0's and hvl1's...