I second Sheriff of Nottingham. It's a very clever game in which each round a player will take the roll of the sheriff. The other players look at their hand of cards and place their chosen cards (goods) into velvet bags and pass them along to the sheriff, stating its contents. The rub is that not everything you may be giving the sheriff is legal. There may be contraband in the mix. The sheriff has to deduce whether or not the player is lying. If the sheriff believes that you are lying and opens your bag and there wasn't any contraband he owes that player gold! If the sheriff was right, that player owes the sheriff and doesn't get to place any of that contraband on his or her player board. This creates room for bluffing and double bluffing. What's even more fun is that bribes and deals can be made. It's very open ended. There's a set collection aspect of the game to so there's a element of strategy stacked on-top of the social aspect of the game. The artwork is phenomenal as well and the theme really does shine through.
There is a caveat, but it's a caveat that is true for virtually all games with a major focus on social interaction. That is, it is very much group dependent. The majority of games I have played have been loads of fun. However, that doesn't mean I haven't had a handful of not so enjoyable games either. Those less than fantastic games weren't the fault of the game but that the game didn't vibe with that group. If you have a group of friends who are also into social games then I cannot recommend it enough. It really is one of my favorite games to play. Plus, they really do have wonderful customer service.
Another game with a focus on social interaction that is enjoyable is Vault Wars. The premise of the game is simple, what happens to all of that loot adventurers have stashed away in vaults if they die? They up for auction of course! It's pretty much Storage Wars: Fantasy (I've never actually seen the show... but it isn't difficult to discern the premise.) There's some cool little mechanics going on and it comes in one of those magnetic clasp boxes.
One of my favorite social games is actually a co-op game, Mysterium. It's Dixxit but so much better. It's almost worthless to describe, you really should just watch a video review or look at pictures to see how great the game looks. Plus it's as good of a game as it looks.
I've been really into Cthulhu Realms lately. My fiancee and I play it a good bit, in fact I've never played more than two players. I really do enjoy deck building. There's something immensely satisfying when you chain together a bunch of cards. I won't say it's the best game ever made however it's one of the best games in terms of value. For $10 I have gotten a immense amount of fun from it.
