For my husband! Tomorrow!
Yeah, I forgot our anniversary. Eight years. I am a waste of air.
Help me, Dopers!
I need something neat that I can get quickly. Up to $100.
He’s geeky, into science and computers, loves movies and reading.
Anyone? I’m going to go slam my head in a door between checking for replies.
Science and computers and movies and reading. Somewhat vague, but it gives you a lot of options. Does he have a favorite movie or TV series? Pop over to Best Buy or Barnes & Nobles and grab the box set or the first season on DVD. Or a bunch of books about quantum computing.
If you’re not signed up already, open a Netflix account for him. You can do it right now, online, and you’re covered for tomorrow.
You could tack on a gift certificate from CompUSA or something, too, for good measure. I’m sure you could purchase one online, and that your husband would receive email notification of his gift.
You, naked, with a couple of bows, is really all you need. (I know a guy who did that with his wife, and he said it worked like a charm.) Failing that, here’s a handy guide for geeky presents. 
Off the top of my pointy little head, how about a year’s worth of monthly movie tickets for the 2 of you? Kind of a like a date a month for a year, guaranteed. You can buy passes like that at theaters, I think. A note saying he gets to pick the film every time. You could hide it in a tub of popcorn… Other than that, the naked with bows thing would probably work 
Give him card saying how much you like his many interests. The card is your gift certificate, too, worth 100 bucks for him to spend on a few sites you write down. A site connected to a hobby of his, of a site like this: http://www.thinkgeek.com/gadgets/
Does he have a wishlist at Amazon?
Serenity comes out tomorrow on DVD, if he’s a fan of Firefly. 
Or you could just get it for me…
Science, geeky & a man?
Get a Swiss Army Knife. One of the Swiss Champ models. They are killer!!
Order today, & fib (a little) by saying “the order was late”, then show him the online image.
Well, you were late in ordering, right? So it isn’t a total lie.
And the Swisschamps are really nice.
Good answers everyone, and now I’ve got some new ideas for Christmas.
In the middle of the night, I sat bolt upright and said, “Baseball tickets.” I got tickets for the three weekend season opening games for the Cleveland Indians and he’ll be delighted.
But the reason I finally managed to think of something was my attempt to predict what Dopers might suggest. Thank you all!
IF he’d into sports (I’m not): one set of Sports tickets [maybe even a couple for his friends, depending on gis favorite sport) plus the Gol-Darnedest game/tailgate party you can dream up between now and then. Yeah, the party’ll run you over budget, but you can scrape that out of the household budget, and the Food Channel will give you some killer ideas. You must, after all, atone for forgetting. All us guys do.
Then again, I’ve always loved cooking and entertaining, so YMMV.