Small World! races and abilities are paired in almost an endless combinations, especially with the expansions, so we can just keep playing and playing without feeling a repetitive pattern in this game - and the minimal influence of dice are also a plus in my group.
Citadels - for a card game, it is very interactive and strategic, a lot of level-thinking, and it plays from 2 to 8 players! most recommended with 2-4 players, since there's a lot of downtime with more players.
Puerto Rico - like the others have already said, its great! minimal luck, great subtle player interaction, and generally just a nice strategy game.
Dust - my group has been very positive about this Risk-like game, but I do fear that the joy might wear over soon... its fun and aggressive, but it does get a bit the same, plus it takes around 6 hours for the epic ruleset to play (the shorter rules suck!)