Games you can play in the office over lunch need to be small enough to carry inconspicuously, quick enough to finish in an hour or less, and quiet enough (both literally and visually) so as not to gather unwanted attention. Assuming you are converting non-gamers to gamers, you will need to start with some gateway games (characterized by simple rules, very fast rules explanation, and components that don't look "too geeky").
The Resistance (Avalon or the original) is an excellent game and will entertain 5-10 players in under an hour. It's not as easy to teach or as innocuous looking as many of the other games on the list, so you'll want to build your coworkers confidence with less thematic games first. My group loves Avalon a little too much.
Hanabi is one of my favorite games. It's a cooperative card game for 2-5 players (best with 4) with an innocuous theme. It's not hard to teach, but it is hard to play well, especially if one or more players don't commit their full attention to the game.
No Thanks! is a devilish little card game for 3-5 players. It's pretty easy to teach and shouldn't scare off hobby-shy players. That said, it can be pretty cutthroat; It won't appeal to all players and could turn some people off your group if they're not already part of the fold.
Coloretto takes 3-5, and is a perfect gateway game (being teachable in less than a minute and having components that won't scare anyone off). It's also quite deep and a good way to get to learn how your co-workers think.
Wizard is a traditional trick-taking card game for 3-6 and if you can find the version that uses standard playing card faces, you'll have no trouble introducing the game to people afraid of hobby games.
Turn the Tide isn't complex, though its different enough to require a play through to understand. It's a very deep card game for 3-5 players and it has cute pictures of sheep. (You barely notice they're trying not to drown!)
23 is a devilish little card game for 2-4 players. It's pretty easy to teach and shouldn't scare off hobby-shy players. That said, it can be pretty cutthroat; It won't appeal to all players and could turn some people off your group if they're not already part of the fold.