If you want to read more X-Men, I'd recommend checking out Grant Morrison's New X-Men run. It happened basically right before Whedon's Astonishing X-Men, and it's good stuff. After that, check out Uncanny X-Men. The Messiah Complex crossover event is as good a place to start as any, then just read Uncanny straight through to the present day.
If you want to read some Avengers, check out Kurt Busiek's great 1998-2002 run on the series. After that, read the miniseries Avengers Forever. In fact, read everything Kurt Busiek has written on MU, it's all good.
Definitely read all of Ed Brubaker's work on Captain America and Winter Soldier, Matt Fraction's Invincible Iron Man, and the 2007 Thor series by J. Michael Straczynski followed by Kieron Gillen. Make sure you read the Siege story arc, followed by Gillen's Journey into Mystery, it's fantastic.