ME1: Liara & Tali ME2: Garrus & Tali (though Mordin & Grunt are another of my favorite combos) ME3: Liara & Garrus
Really, though, I've played the first two games so many times, all party members received their own dedicated game sessions (especially in ME1, when the game actually rewarded you for doing so). Unfortunately, all the party members that debut in ME3 are too lackluster compared to the familiar faces (IMO), so Javik's the only one amongst them to ever earn a spot on my team.
Sidenote, I'm glad the Citadel DLC gave me the opportunity to roll with the dream team of Grunt & Wrex, even if only for the Arena. Give 'em both Claymores, and I don't have to do a thing. Everything. Dies.
Is that supposed to be your head between your shoulders? I thought it was a kumquat. - Oda Nobunaga