I'm going to go out on a really geeky limb and shout out my love for Patrick Steward as Captain Jean-Luc Picard.
The 9th & 10th Doctors of the new Doctor Who both has an awesome level of well over 9,000, but the 10th (David Tennant <3<3<3) wins for me.
And for the odder mentions, Garrus of Mass Effect along with Mordin Solus. I think the husband was actually jealous of a non-human videogame character for a while.
Summer Glau - Seconded!!
And Lexa Doig from Andromeda.
@Micael Steven Martin
"I look like a Jewish horse/monkey. But I'm pretty OK with it." - Sarah Silverman
This may fall outside the realm of geek crush and more into the growing-up crush category, but I'll go with Winnie Cooper (Danica Mckellar) from The Wonder Years.
On second thought, maybe she should count as a geek crush; she has written 3 math books!