Best Light Strategy Party Games?
There are of course different definitions of light strategy games, so I will just mention some games, which I have introduced to nongamers in parties, and which have been interesting both for them as well as more experienced gamers (in random order).

Games which can be explained in 5 min

Small pure card games:


Saboteur: 3-10 players, 30 min
6 Nimmt! or Category 5: 2-10 players, 45 min (usually less)
Coloretto: 2-5 players, 30 min (this one I really like despite its simple rules)


Cards and some bits:


Citadels: 2-7(8 with usually included expansion) players, 60 min - this one is a must have
DiXit: 3-6 players, 30 min - almost no strategy but very good and can be easily played with upt to 8 players even using just the expansion and writing points down on a paper


Abstract:


Rumis(+): 2-4(6 with expansion) players, 45 min
Blokus: 1-4 players, 20 min


Other:


Ca$h'n Gun$: 4-6 players, 30 min
Fast food or any other reaction game like Halli Galli, jugle speed are all around 2(3)-6(8) players and 10-15min
Roll through the ages: the bronze age: 1-4 players, 30 min (this is a nice gem, also pure gamers love it, and when you have taught all others some games and don't have anything to do, you can play it by yourself ;))


Games, that require a little longer explanation, but are still manageable


Bohnanza: 2-7 players, 45 min. Even though this is an easy game, explaining it always takes me more time than I like
Bang!: 4-7 players, 30 min. This one is really good for more players, but explanation takes some time. Can be modified so, that healing beer cards make the player drink a tequila shot ;)
Dominion: 2-4 players, 30 min. Everybody loves this one, and it can be played as fast filler. Just don't overdose with expansions in the first session. If you have an expansion, you can run more than one parallel game.
Agricola (Family version): 1-5 players, 120 min. If you are really adventurous explainer and have longer time to kill in a small party, this actually can work really well. My nongaming in-laws understood the family version on ~10 min and really liked it (even though their score wasn't great)
7 wonders: 2-7 players, 30 min. As previously mentioned it might look intimidating, but is easily explained and a fast game.


In my opinion one of the most important things for a game to be successful with non-gamers and casual gamers is the capability of "getting in the game fast" - you must generalize the important rules and guidelines and delve into details as you go. If you do so, and the game is not a total brain burner and doesn't exceed some 2h, you will be able to play almost any game with nongamers.
Basically:


Persuade them, how cool the game is
Don't scare them away before they get into it


Also, a good advice by Tynam - with some exceptions, like bang and saboteur, try to split the group in several smaller gaming sessions with similar expected game time, so they can mix the games during the evening.

Edit: Added hyperlinks as promised