I also really enjoyed Citizen of the Galaxy, Heinlein is a good writer. It's been years since I read it, but I just skimmed through a synopsis and a lot of it comes right back.

I can't come up with a favorite unfortunately, but I'll list a few close to the top of my list. A few Heinlein books to start off!

• The Moon is a Harsh Mistress - Robert Heinlein
• Starship Troopers - Robert Heinlein
• Dark Matter - Blake Crouch - This is one of my favorites. Highly recommend if you haven't read it yet.
• Dune/Dune Messiah - Frank Herbert - I really enjoyed the first two books, but kind of lost interest later in the series.
• Daemon - Daniel Suarez - Really interesting book. The sequel, Freedom, is also good.
• Altered Carbon - Richard K. Morgan
• The War of the Worlds - H. G. Wells

There are a lot more that I like, but I have to stop somewhere!

Oh yeah, there are plenty of SF readers here. I read everything Heinlein wrote when I was growing up, and have gone through re-reads of most of it. Citizen's solid, though The Cat Who Walked Through Walls is probably my favorite.