There are a number of episodes that I find really inspirational.
The first one I can think of is "Not Fade Away". I love that episode. Just about everything in it I find inspirational, especially the end. The final scene in the alley is just incredible, and Angel's last words of "Let's go to Work" gets me every time.
"Hero" is another one I really like. I don't think they could have come up with a better send off for Doyle if they tried. Doyle's last scene with Angel, where he tells him that he finally truly understands the good fight, and his kiss with Cordelia gives me chills.
"Chosen" is an awesome finale. There are problems with the episode, but metaphorically it's outstanding. THE best soundtrack of any episode of either series. Seriously, the final score in "Chosen" is amazing, and really epic. It starts off awesome with Caleb and Angel and it ends just as good.
"I Will Remember You" and "City Of..." are two others I find really inspirational. I'm a sucker for the moments where the hero isn't afraid to sacrifice everything to do what's right, and that exemplifies Angel perfectly.