Well, my wedding wasn't geek themed, but "my" cake (the groom's cake) was shaped and decorated like a red dragon. It had chocolate horns and everything. It was red velvet cake. It was quite tasty.
My groomsmen and I wore kilts, which isn't geeky, just bad-ass. And I wore a very sharp, foot long Scottish dirk on my belt (not to mention the sgian dubh in the sock). Some might consider that to be geeky, I guess.
Some friends of my wife had the musicians play the Darth Vader theme song as they walked back down the isle after they were married.
Not terribly geeky, but I officiated my best friend's wedding a few Halloweens ago wearing the get-up of a voodoo priest and the wedding party was dressed in 20s style outfits.
I attended a (real) wedding that was held at a SciFi convention in Atlanta (so that all the couple's friends would be able to attend). The wedding party wore Star Fleet uniforms, and the minister dressed as a Vulcan priestess. The mothers of the bride and groom were these two little old ladies who looked like they had no idea what any of it meant, but they smiled all the way through.
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For my own wedding, I wanted to play the Imperial March from Star Wars as my wedding march (i.e. as the bride entered), but I chickened out and went with the traditional music instead.
I used to work with a guy who officiated a geek wedding. The bride and her party came dressed as the Emperor's guardsmen out of Star Wars and the groom and his party came dressed as redshirts.
Sounds like I'm going for a renaissance faire wedding. Next year. I need to make my dress (my faire costume has seen better days) and he needs to decide whether he'll dress as a dude or as a horse.
Not a complete geek theme, but at our wedding, my wife and I had the Throneroom theme from Star Wars play as our recessional. My groomsman had to restrain himself from doing a wookie-yell.
Some of our friends had Zelda music during their wedding ceremony.
My newest wife put the kibosh on any geeky plans I may have had. My first wife stopped my friends from getting fantasy themed costumes for everyone involved. SO I struck out twice. this is just so sad I am going to go to a corner and whimper..........