Here's the MagicShine:
http://www.geomangear.com/index.php?...1vdep209pssr36

It's not really 900 lumens, if I remember right it's like between 400-500. And the battery isn't waterproof, people who ride in the rain have added waterproofing (by sealing the holes in the battery casing or putting it in a bag). It's also $85 (probably before shipping).

If you want something more durable, a Dinotte 200L takes AA batteries and puts out 200 lumens for around $100. Easy to move from bike to bike, but obviously it's about half the light output. A very solid build.

Dinotte makes some other lights, but if people want the "ultimate but affordable" light, I've really liked my Light and Motion Seca. I bought the 700 (only had it for 2 weeks), and frankly I almost always just run it at half power, so I'd suggest the Seca 400. But - we're talking seriously more money. The Seca 400 is $400 (retail). I'm just trying to be complete by mentioning it - of non-dynamo lights, it has the best beam pattern (a beam that fairly evenly lights the road surface), the best light color (it's more normal looking light than the usual blue you get with LED's), and it doesn't waste a ton of light throwing it up into the trees. But...we're talking about way, way more expensive there.

The MagicShine is a very, very popular suggestion here on bikeforums because of it's price to light output ratio, even adjusted for marketing hype. I'm not familiar with how much light a 20 watt halogen puts out, but I'll take ItsJustMe's word for it that it isn't a lot. From the sounds of it, a Dinotte 200L would also put out more light than you currently have, with better build quality (though be prepared to use rubber bands to keep the AA batteries in their holder). But I've ridden mine in rain, in the winter, etc and it shows no wear. And of course, if you had money to spend I really like the Light and Motion Seca's.