Party Poker is one of the biggest poker rooms in the world, with traffic, promotions, tournaments and game selection all top tier. Party Poker is also known for running tons of satellites and special events, including the famed PartyPoker Million. Because of the good traffic and game variety, any player can typically find a table they like - particularly if they're looking for soft Hold'em action. Sign up through a PokerListings link and receive an up to $500 bonus at 100% match.
Poker1.com is the home of Mike Caro's University of Poker and other online resources. It presents the "University" with 43 (!) lectures, test and strategy articles. There are also a lot of material on odds, rules, audio/video clips, tips and other. Also offers shop and forum. Very high quality and broad scope in the online strategy tutorials. Highly recommended!