It's Monday, and some of the funnier shows I like on TV are on. I noticed that the CBS lineup is actually three Nice Guys in a row!
On The Big Bang Theory, I find Leonard to be actually a fairly self-aware Nice Guy, and definitely the geekier variety of the species.
Then (my favorite show of the three), How I Met Your Mother features Ted Moseby, who shows his NG credentials with his incessant need to be in a romantic relationship, whether it's a good one or not.
Finally, we have Two and a Half Men, where NG Alan Harper is usually bitter both about not getting what he wants, but also about his brother Charlie (basically, the shadow/opposite of a NG) getting everything he wants.
There are lots of other NGs in past TV shows. The wikipedia entry for Nice Guy had once listed George Costanza as an NG - which I found to be wrong! (I don't feel nice about that).