When I was about 12, I do freely confess that I had a crush on Holly Marshall, from Land Of The Lost. :o
And, if the LOTL fansites I’ve checked are any indication, so did a lot of other little boys.
Holly seems to have been the femme fatale of the Middle School set. 
So, what TV characters did you have crushes on, in your Middle School years?
You are all going to laugh. Please remember I was eleven when TNG came on.
Wesley Crusher.
Yes, the character was annoying, but I still think he was kinda cute.
Don’t remember any TV characters as much as I remember Joey Heatherton urging me to be a pefect sleeper…
Erin Grey in Buck Rodgers. Bidi bidi bidi.
I had a huge crush on Emma Peel from the Avengers. The show was on in reruns when I was a kid.
Also, Mr. Kotter’s wife on welcome back Kotter and Daisy Duke.
Laurie Partridge was soooo dreamy!
Oh wait, middle school? Jodie Foster, I guess. In high school, I had a thang for Angels.
Lucas from SeaQuest DSV.
RIP, Jonathan Brandis. 
I opened this thread expressly to mention Wilma Deering/Erin Grey, only to be out-drawn by Loach. Damn you! :: shakes fist ::
Sigh. Shgoratchx! just might have been the best episode evah!!
Aliens: “Off think, off think”
Me: “Go, you horny little men!”
Joy (Caroline Ellis) from The Bugaloos.
Laura Petrie (Mary Tyler Moore) from the DFick Van Dyke Show, of course. I think a lot of guys my age were smitten by her.
And Emma Peel (Diana Rigg) of the Avengers, as noted above. Looked good in a catsuit, was smart, and had that British accent. Yum!
Daria and Maleficent from Sleeping Beauty.
Keith Partridge. I still love him.
Anthony Russo, from “Blossom”. He was smart and kind, but with a bad-boy background (he was a recovering drug-addict). Then he married a black woman whom I could live through vicariously (even though I’m not a woman).
Kelly, the beautiful sidekick in the short-lived Robert Wagner secret-agent TV series “A Man Called Sloane.” Smokin’ hot.
Margaret Houlihan from MASH.
Allie’s daughter from KATE & ALLIE. (Not to mention Kate.)
And, Jane Parker as played by Margaret O’Sullivan. (Yes, I know she wasn’t a TV character, but I only saw her on TV.
Oh! And Lieutenant Uhura.
No crushes, as such. I had middle-school erections over Donna "Ellie May " Douglas and Barbara “Jeannie” Eden, though.
Just to make you guys feel good: Erin is a regular at the San Diego Comic Con and she still looks great. I mean, she has aged better than any other woman that I can think of (like a female Dick Clark). She does look a bit older, but it’s like she stepped out of a time machine or something.
As for my crush, “Bridget” - Meredith Baxter Birney, from “Bridget Loves Bernie” (later went on to “Family Ties”).
And, of course, Bailey Quarters from “WKRP”
In my mid-teens, I had a thing for Lydia (June Chadwick) from the V television series. Go figure. Musta been the eighties-hair thing.
When I was much younger, I liked Nova from Star Blazers, which is interesting, since I’ve never been a huge fan of Leiji Matsumoto’s art style.
Well the first and most obvious one is Sam from Who’s The Boss. She was cute and athletic. I dug/dig that.
My biggest crush was probably Six from Blossom. Again, she was a cute girl and seemed nice.
Wanda from ‘Doogie Howser’