I have a few, but most have changed over time. I think my first heart-throb, in the 50's, was Pat Boone (don't laugh!)
Others have included Paul Newman - I'm a sucker for blond hair and blue eyes, and also Christopher Plummer in 'Sound of Music' but not in anything else.
I also like the tall, dark and handsome guys - Hugh Jackman in 'Australia' was wonderful, and in 'Kate and Leopold' (a time-travel movie), and also as Curly in the National Theatre production of 'Oklahoma' (the guy can really sing too!), but I'm less keen on his rippling-muscled Wolverine.
Colin Firth is another gorgeous guy - I fell for him, not in the much publicised 'Darcy exits the lake in wet shirt' scene, but when he was watching Elizabeth playing the piano. My God, those dark eyes of his said everything - hot, hot, hot! I had to stop the DVD and play it back several times while I drooled. Actually I fell in love with Darcy originally when I first read P&P in my teens. Mr. Rochester was another of my teenage favourites. Anya Seton's 'Katherine' inrtoduced me to the wonderful John of Gaunt, and who could fail to love Richard III in Sharon Penman's 'Sunne in Spendour'.
But of course my all-time favourite (as you know) is Martin Sheen. I fell for him way back in the 70's when he played John Dean in the Watergate mini-series 'Blind Ambition.' I now have over 100 of his movies on DVD or video, some brilliant, some appallingly bad (although his performance never fails to impress, however bad the movie as a whole). In the 1980's he was especially attractive (for that read: "totally gorgeous") and he made some good movies during that period. And I fell in love with him all over again when he played President Jed Bartlet in 'The West Wing' (the "best President America never had"). I owe Jed Bartlet a debt of gratitude because it was wrting West Wing fanfic that got me back to writing novels again.
As far as my own writing's concerned, I've been in love with each of the heroes in my stories. I think you have to be, otherwise the reader won't fall in love with them either.