While I completely agree with logic behind playing 1...e5 (it really
is important to learn how to handle open positions) I'd have to disagree with it as a suggestion; considering the request was for
"something that doesn't have too many variations to memorize, and something I can use too play for the win"
I don't think 1...e5 fits into this category.
I personally started playing the Caro-Kann recently (thanks to Peter Wells) and think its a
great defense. I wouldn't bother switching if you know it already, but would focus on tactics at your level. That should yield more points than any new repertoire. But I digress...
If you really want something new, the Scandinavian is a good suggestion (especially the 2...Qxd5 lines). But I wanted to add that if the
main criteria are "not theoretical" yet still "double-edged" I'd probably suggest you check out
Play 1...b6 which was written by Christian Bauer.
You can read more about it in previous threads or the link:
http://www.amazon.com/Play-1-b6-Dynamic-Hypermodern-Opening/dp/1857444108/ref=sr... Black gets an interesting game with almost no theory. It also puts most white players out-of-book within a handful of moves and that's usually good news.
Of course, I don't think Black can equalize as easily as in the "real" defenses (e.g. the Spanish, Najdorf, French, etc.), but its
very hard to play such lines without a ton of theory. Also the critical lines of such major openings tend to lead to very complicated middlegames which are hard to play OTB, even if you
do know the theory to reach them.
With 1...b6, you have "light-square restraint" in mind. Eventually you counter-attack the white center via ...f5 or ...d5 breaks. It's not exactly rocket science (and certainly not as respected as mainline stuff) but even the lines where white is better are not
that bad for black (i.e. the middle games are playable). So, I think it meets your criteria rather well.
I had plenty of success with 1...b6 a few years ago, but I gave it up simply because it's not a "real" defense to 1.e4 and I figured I really ought to learn a "big boy" opening. My style also became more solid, in that I stopped wanting to give white such a free-hand in the center or a clear spatial edge. So, I began to play the Petroff against 1.e4.
But I got tired of all the crazy gambits and "anti-petroff" stuff I would inevitably face OTB. (i.e. the Four Freakin' Knights

) Then after a few "flavors of the month" I got into the Caro-Kann, which I think will be my main defense for awhile now.
So, just to be clear, I think the Caro-Kann really is objectively better than 1...b6, but I also think its mostly important to play whatever defense you enjoy and are comfortable in. I think you'll find you're not losing many games because of opening preparation as much as tactics. But check out Play 1..b6, and hey, if nothing else, the book presents interesting games annotated by a very good writer. that's my free advice...