I didn’t have the famed Farrah poster. I had Star Trek posters all over my walls. Then, a few large prints of B&W classic shots, by Adams and Bresson, then B&W photos I took of GF.
Farrah…wayyyyyy too scrawny. 
Oh, this is somewhat troubling…
I had crushes on:
Lt. Columbo (Peter Faulk),
Barretta (Robert Blake)
Gomez Adams (John Astin - The Adams Family)
Quincy (Jack Klugman)
Wait! Somebody remotely attractive!
Andy Travis (Gary Sandy - WKRP)
Earliest one I can remeber was Kari Wuhrer on MTV’s Remote Control, made my 6th grade brain spin.
Also had a thing for Sherilyn Fenn in Twin Peaks, a title which led to endless teen-age innuendo.
James Franciscus, in Longstreet
Well, I thought Shawn Cassidy was way cute, but my best friend already had dibs on him, so I got stuck with Parker Stevenson, the other half of the Hardy Boys. He wasn’t so bad, more handsome than cute (like Shawn was). He was plastered all over my wall in fifth grade.
The first one I remember is Mark Paul Gosselaar on Saved by the Bell when I was like 10. Both on reruns and The College Years.
He’s even hotter now, is the thing.
Joy…Bugaloos
Holly…Land of the Lost
On The New Adventures of Huck Finn, Becky Thatcher was played by Lu Ann Haslam. You can see some photos of her here.
Lisa Gerritsen indeed played both Lydia on My World… and Bess on MTM.
Most of my crushes have already been mentioned – Maureen McCormick, Valerie Bertinelli, Lynda Carter, Farrah Fawcett. However, I’ll add (from Petticoat Junction reruns) Lori Saunders, who played Bobbie Jo Bradley. Be sure to scroll down that page for an alphabetical (by first name) list of more “Classic Babes”.
Bill Bixby as Tim O’Hara in My Favorite Martian.
Also there was Ken Berry as Capt. Wilton Parmenter on F Troop.
You can keep Mork but bring me Mindy!
Also Cheryl Ladd. (now I can lust after her daughter!)
And my weird one would Penny Marshall as Laverne De Fazio.
Ok, my very first super crush was Robert Horton, who played the scout Flint McCullough on Wagon Train. God, I loved that man. I had a cheap metal necklace in the shape of a heart that I got at the county fair. It had my name “engraved” on the front of it by one of those cheap little vibrating “engraving” pens. I used to write “Flint” on the back, on the side next to my heart.
How sad that! Of course, I was very young.
My love affair with Mr. Spock lasted for many, many years too. After I got over Flint.
David Canary as ‘Candy’ Canaday.
Right. Here goes…
Jenny Powell (No Limits)
Kathy Evison (Seaquest)
Leslie Bega (“Maria” in Head Of The Class - I suspect I could regret that one)
Diana Rigg (The Avengers)
Diane Oxberry (obscure presenter on Radio 1 and Saturday kid’s TV, the photo here looks nothing like I remember her)
Sadly, I know for a fact there are more I can’t remember right now.
And there was also the Professor on Gilligan’s Island.
Kristy McNichol and Valerie Bertinelli.
Another Valerie Bertinelli fan here. I also had it bad for Justine Bateman, who was Mallory on Family Ties.
No one’s mentioned Kimberly Drummond (aka Dana Plato)?
Jaclyn Smith (Kelly Garret).
Angela Cartwright (Penny Robinson).
Kim Richards (Tia in Disney’s “Escape from Witch Mountain”).
Lauren Tewes (Julie McCoy - and this illusion was cruelly spoiled years later when I met Ms. Tewes in L.A.)
And an unaccountable and unhealthy fascination for Susan Tolsky, who played Biddie Cloom. I can’t explain it.
Oh… not a crush, but every time I see Leelee Sobieski I stare at her as if I were a mental patient, but that’s not out of lust or crushiness of any kind, but because I am fascinated with how much she looks like Helen Hunt.
John Schneider crush chiming in here, belonged to his official fan club and everything.