Kaiden in ME1 (but he died), Liara in ME2 and Jacob--somehow.  I don't remember how.  For some reason, when I played ME3, I remember getting with both of them.  Maybe it was from two different playthroughs.  I just remember that Femshep was pissed at Jacob when he found somebody else in ME3 and she kissed Liara when they met in ME3. In ME3, Specialist Traynor showed up and seduced me (that whore!) and then Liara got really pissed at me.

I never really thought about it.  Maybe I got with Liara in my "official" ME1 save or something.

Your Shepard's relationships sound super complicated

Did Liara really yell at you? Man! I've got to try cheating on one of my squadmates at some point. Miranda didn't yell at me when I cheated on her with Cortez

Yeah, it was like twenty seconds after I had sex with Traynor in the shower.  I was like, "Hmm.  That was unexpected yet, satisfying..." then I went to talk to Liara and she was like, "I heard about you and Traynor.  It's over between us!"  and then she acted bitchy towards me for the next few missions.  I don't know who it is that keeps running their mouth about my sex life on the Normandy but it's pissing me off.

In ME2, right after I got with Jacob, one of the women (I think it was Kasumi) was like, "Oh, I heard you and Jacob did it!  You're living the dream, huh?"  And in my first playthrough of ME2, I kept going between Garrus and Thane but neither would touch my skanky Shepard poontang until I broke it off with the other.  I wound up getting with Garrus ("Well.....that was....interesting....").  I wish I would have kept THAT scenario for my playthrough of ME3!  It would have been interesting. 

I tried getting with Miranda and Jack in ME2 but apparently, they aren't into that kind of stuff.