I'm a big fan of party games.  Especially when you're with a group of people who would never seek the moniker of "gamer", these light and fun games can liven a gathering and bring people together in a way that few other activities can.  And in my opinion, party games are the red-headed stepchildren of the gaming world.  They get little respect, but I think they are a powerful weapon in the arsenal of any game-group organizer who wants to be able to match the right game to any particular group of people.  So anyway, here is my opinion of what are the top 10 "must-own" party games!

Runner Up -     
Werewolf / Mafia

This is a runner-up mainly because you really don't need to "own" it to play.  Sure, there are several versions that have been developed and professionally published, but all that's necessary to play is someone to explain the rules and serve as a moderator and then some method of choosing who will fill the roles of Werewolves/Mafia and Villagers/Innocents (such as a deck of regular cards).  Of course, there are tons of optional rules and roles that can be included, and you can make it as simple or complex as you want.  It is a great game of negotiation, bluffing, and persuasion, and the only drawback is that some people have trouble getting into either the negotiation mechanics or the "role playing" atmosphere of the setting.  Still, this is great to introduce to any group just to see how they'll react.   

Number 10 -
Apples to Apples

This is a perfect example of a very simple concept that caught fire in popularity.  Just pick the noun from your hand that best matches the adjective on the board, then let the judge choose which one they like best.  It is so good because almost anyone can play, it can be taught in seconds, and it can be a laugh a minute.  Personally, I've never had a circumstance where it's really "made the party", but I find it to be a good way to bring a lot of diverse people together.    

Number 9 -
Pit

I fully admit that Pit is not for everyone.  It is extremely chaotic and can get quite loud, but it also produces a genuine rush that I have rarely experienced elsewhere in gaming.  And for a group with which it "clicks", it is absolute fun on a stick.  I've played for years, and definitely recommend getting a version with a bell, both for thematic reasons and to help settle cases where multiple people corner a market at the same time.  Of course, you'll eventually need to buy another deck anyway, because the game itself can be pretty tough on simple cardstock. 
    
Number 8 -
Imaginiff

Imaginiff is a game about trying to pick the best description available for an identified person.  You score by matching the other players with your selection.  This is one of my favorite party games, but it has one significant limitation, that you really need to know each other pretty well to have a good time.  This can be somewhat mitigated by using famous or other commonly known people as the subjects (instead of the people playing the game), but you lose a little bit of the "ownership"/buy-in to game play when you do this.  Still, for a family or group of friends, this is great.

Number 7 -
Wits & Wagers

This is a relatively new game to me, but it has been a big hit from the start.  It is a trivia game where knowing the answer is not necessarily the most important skill involved.  After you write down you answer (which is always a number, by the way), you arrange them in order and then make bets on which is the closest to being right without going over.  Those who do well at estimation, playing the odds, and knowing the people (and their relative knowledge about certain topics) tend to do well.  I've also noticed that this goes over a little better with men than women.

Number 6 -
Catch Phrase

While it's not my favorite game, this is the one that everyone really should own.  It's a perfect cross of password with "hot potato" that I have never had fall flat.  It can single-handedly turn a regular party or game night into a great time.  I've heard some people say that the electronic version is better, but I tend to find that the good old analog version is better for me (mainly because the scoring buttons seem to confuse peope on the electronic version).  There are some who just aren't good at password games, but even they get caught up in the tension and excitement of this true classic. 

Number 5 -
Scene It - TV

The Scene It line games is another great example of a trivia game that can be entertaining to people who aren't very good at trivia.  Most of the DVD mini-games are non-trivia-related, and even with the video clips it is more important to be observant about what is going on than to know everything about the show/movie itself.   Personally, I think that Scene It-TV is a little better than the original both because it has a little better production quality than the original and because the average person probably has more exposure to TV than to a wide array of movies. 

Number 4 -
Scattergories

This is a very popular classic that I never get tired of.  It is different than most of the other games on the list because it is usually a very brain-burning individual effort.  Still, it can be played with partners (which makes it a litte easier and allows more people to play), and it has a great potential for fostering creative answers.  It's a very cerebral game, but one that still has a lot of laughs and fun in the scoring rounds.  The only drawback is in the "judging" part of the game, when the group has to decide when a questionable answer will count or not.  But in general, there are few othe party games that I enjoy more. 

Number 3 -
Liar's Dice

I've mainly played this in groups of four, but it can easily be expanded to as many people as you have dice and cups to accomodate.  It is addictive and intensely fun, but also has a few problems.  First of all, not everybody enjoys the bluffing/betting/reading skills involved, which you can't do much about.  Second of all, player elimination is a big part of the game.  This isn't a big deal because you can always just restart a new game with the first four or so people eliminated, and frankly, it's actually a pretty fun game to watch.  

Number 2 -
Taboo

This is both my favorite partnership and password-style game.  It's still great with groups, but my wife and I can just get in a "zone" where we are practically thinking the same thoughts when we play together, and it is just fantastic!  The idea of having the "taboo" words that you can't use when giving clues is just so brilliant and simple, and I think it makes for a great balance between challenge and fun.  There is definitely a skill involved with giving clues, however, and some people have a tough time getting over the learning curve.
    
Number 1 -
Balderdash

To me, Balderdash is everything that a party game should be.  It is fun, funny, and does actually involve a little skill.  The only (minor) problem is that it can take a while to play, because people have to have time to think about their responses and then to read them all aloud.  But the payoff for that time investment is more than worth it.  What I think is so cool is how this game, unlike most other party games (or most board games for that matter), seems to generate stories about the game session itself that get retold time after time.  It promotes creativity even in people who aren't usually very creative, and is almost always absolutely hillarious.  It can take a little time to figure out how to word things to make them sound like how the cards are written, but the variation on the cards themselves alleviates this to some degree.  Balderdash is not only one of my top 10 favorite Party Games, it is also one of my Top 10 favorite Games of any kind! 

So anyway, I hope this is useful to you.  If you have any questions about any of these games or anything else concerning party games, feel free to ask and I'll do my best to give you an answer!

Happy Gaming!