Museums? Planitaria? Tours of sewage treatment plants? Dinosaur digs?
If you were making a list, what would have to be on it? And is there a prime example of it in your neighborhood?
Geece.
As a firmly entrenched member of the geek camp ( I own a computer shop, do they get geekier 
)
My personal fave, especially if you have never been
Las Vegas
Tons of applied computer wizardry to ponder, the star trek experience at the hilton, tons of museum and historical recreations of landmark goodness, shooting ranges that allow you to fire full auto weapons, go during CES or another big electronics event and you could be up to your eyballs in geeky goodness for days.
I see you’re familiar with the Musée des Égouts de Paris
The sideshow?
Does birding count? Does it count if you go out of your way (say, drive several hours each direction and camp overnight) to go somewhere specifically because of the birds?
Gencon (a D&D/gaming convention). I’ve been two or three times, and it’s transcendantly geeky and transcendantly fun.
Science museums are pretty great.
The Galileo museum in Venice was pretty cool, as was the glass blowing island. Pompei is also pretty cool to see.
Akihabara is geek central on the planet.
You could always just stay home and try and build something wacky.
I once went on a tour of a company that made sewage pumps. It was oddly interesting. Really, seeing any complex factory machine in person is pretty cool.
Paintball.
I make a yearly trip to Origins myself but the principle is the same. There’s a handful of super-large cons that are vacation worthy for geeks such as the San Diego Comic Con, Tokyo Toy Fair, Essen Game Show, Worldcon, and so on.
I keep meaning to stop at the Mammoth caverns on my way back from Origins but the con is inevitably right in the middle of my busy week season so I can’t afford to take the extra day. One of these days I’ll get to say xyzzy there.
Last year I went to the Penny Arcade Expo. http://www.pennyarcadeexpo.com/ Three full days of video gaming goodness 
I got the best of both worlds. I toured the Ethel M chocolate factory in Las Vegas, and was pleasantly surprised that they included their wastewater treatment system in the tour.
Living history museums. I work at one and I plan on visiting a lot more. Seeing as many as possible in the next two years is my aim. Geek-out, and tax-deductible!
These are great. I am bookmarking this thread.
That is definitely a geek vacation. Are there websites that list good places for beginners to go?
To Left Hand of Dorkness, Gencon is not A D&D/gaming convention, it’s THE D&D/gaming convention. I think I’ve been to four of them.
To the OP, I did in fact tour a sewage treatment plant while on vacation. On Maui. Fascinating. But alas, not open to the general public.
The Bodies Exhibit
Ripley’s Believe It Or Not Museums
DisneyQuest
CES
American Museum of Natural History
Kennedy Space Center
Not uber geeky, but all I can think of.
Also the place for trading card games. If you prefer board games (like I do) I’ve found the atmosphere at Origins to be the better place (though I’ve never had the spare cash to go to Essen… maybe next year…).
Try reading this and following the links for places to go:
http://www.birding.com/beginning_birding.asp
Also, if you google your state and “audubon society” or “birding”, you should be able to find the names of some local birding clubs, whose websites often have lists of local hotspots, group field trips planned, common local birds, etc.
Bytheway, with that combination, I bet you’ve never looked at Tootsie Rolls the same way again. 
horsetech, an amateur bird nerd
The Amazing Meeting 7
A conference on critical thinking in… Las Vegas!
This is assuming critical thinking is geeky… Hmm.
You know what else attracts geeks? SCUBA diving.
Las Vegas just keeps coming up, doesn’t it? Who’d have thought. Does it get to be the geek capital of the US?