Since Neverwinter Nights 2 is easily found these days, I say go with that. Gold edition of course.
Once you get passed the fact its not as good as Baldurs Gate, you actually discover some pretty decent gaming.
Its very true to the D&D 3.5 rule set which, (much to dismay of hardcore D&D players) is actually very enjoyable and relatively easy to understand, especially for newbies.
The latest patches and camera controls make the game much more playable, and the ridiculous amount of character customizing you can do should keep you busy for a while.
And if you find certain parts a tedious grind, you can easily cheat to make it faster and more action-packed.
I generally dont condone cheating, but I also dont condone slow, monotonous gameplay. Giving each character high stats and a buttload of feats can make gameplay much more interesting.
As for older stuff that isnt supported anymore or difficult to find:
The Forgotten Realms pack which inlcudes BG1 & 2 on DVD, Icewind Dale 1 & 2 and the CD version of the crummy game Neverwinter Nights 1.
Deus Ex which is now easily found on Steam, but still needs you to install some custom, home-brew patches to get the game working great.
Vampire - Also on Steam.
Knights of the Old Republic 1 and 2, both of which could be found on store shelves IF you know where to look. Last time I was wandering around Target I found KOTOR 2 for 20 bucks.
Havent played Mass Effect yet so I wont comment.
Everything else available now is hack'n'slash, psuedo-RPG crap. Avoid it if you dont want to be let down.