She was one of the three main cast members (Neil Patrick Harris, Nathan Fillion, Felicia Day) in Joss Whedon's amusing "Doctor Horrible's Sing-Along Blog" miniseries.

https://www.youtube.com/watch?v=IUvPfZqEftI

It actually pains me that there may be people out there who have not watched that.

She's also the voice of Zojja in Guild Wars 2.