Sheppard sure is pretty, but doesn't really do it for me the way Rodney and Carson do. But yes, McShep is the most popular slash pairing in the fandom. Speaking of Ronon... Ronon/Sheppard appeals to me a lot. There's some really good fic for that so check them out on the Crossroads rarer pairings index.

And yeah... Carson. I cried like a baby and haven't really found my SGA mojo since. Though I am writing something for sga_santa again this year (another comm, whose fic masterlists you might want to check).