Well, being a hacker I am, I made my girlfriend an LED heart few years back but if you don’t like hacking, you can get this USB Plasma Heart for Valentines. (via cg) Of course, there’s no guarantee that this will satisfy her over other jewelry options out there.
There’s also an LED Heart-Shaped Pillow, that could be a good alternative.
Instructables has bunch of DIYs on how to make Valentines Treats, so check that out too.
If you are green eco-conscious person, make sure to check out Valentines gift ideas from Treehugger too.
If you run out of ideas, there’s also bunch of Valentines gifts over at Amazon here.