I wouldn't bother with BFBC2, Borderlands, or L4D(2) unless you have friends who will play with you. BF3 will displace BFBC2 for multiplayer and all 3 games have weak single player offerings. BFBC2 has mediocre scripting, especially compared to COD, Borderlands is tedious and a sloppy console port with FOV and mouse lag issues and unsatisfying gun-play in general, and L4D bots just aren't very much fun to play with. Your list is a good start otherwise.
Some other recommendations:
Hitman: Blood Money (about a year older than TF2, but still good
The Witcher/Witcher 2
Wolfenstein (between mediocre and good, but may be worth a play through if you can find it for cheap)
Singularity (a bit better than Wolfenstein)
Alpha Protocol (sometimes buggy and frustrating, but entirely worth it for the story and can usually be found for ~$2 on sale)