You have 30 minutes...

[slinkyturd]

Hitman Blood Money is always a good one for me to play for a level or two.

[ClodBuster]

Super Mario Bros. on NES or the All-Stars port of it. Shouldn't be too hard to beat the game within half an hour.

[Necromancer]

Hatris, Atlantean, Santatlantean, or the 2/5 minute modes in Soldier Blade, Super Star Soldier, etc.

[bob]

Hatris, Atlantean, Santatlantean, or the 2/5 minute modes in Soldier Blade, Super Star Soldier, etc.

(thanks for moving)

[seieienbu]

Good call with a racer.  I do go to Chase HQ quite a bit.

Fix the aspect ratio!

30 minute fix = Battletoads (NES)

I don't think I could play Battletoads for a half hour.  Every time I've played the game lately I get to either the elevator level or the...uh...big wheel level?  Something tells me it's called the "clinger winger" or something similar but that just seems too ridiculous for words. 

Whatever, Battletoads seems like a game that I'd have to cut short if I had to quit in a half hour...

[sirhcman]

Whatever, Battletoads seems like a game that I'd have to cut short if I had to quit in a half hour...

If you warp you should be able to pound it out at around 30 minutes (give or take)

Clinger Winger is the big wheel level, pretty easy as long as you aren't playing on a lcd and introducing lag into the mix.

[seieienbu]

I've beaten it two times in my youth and once as an adult.  You must be a good deal quicker than me if you're beating it in a half hour!

 

[Punch]

If you warp you should be able to pound it out at around 30 minutes (give or take)

"PCEFX member discovers 1 weird trick to beat battletoads... the secret RARE doesn't want you to know!"

[wildfruit]

Advance wars is a great game for a short play. Turn the battle animations off to save even more time!

[TR0N]

Salamander
Metal Slug
Outrun
Magical Drop 3

[deadly_duck]

Usually I see how far I can get in Castlevania 3, but I will also knock out some Windjammers or PuyoPuyo

[reno5]

Beat few dungeon in Dungeon Explorer.

[DragonmasterDan]

Outrun
Tetris Attack
Mike Tyson's Punch-Out
Super Mario Kart
NBA Jam

[jtucci31]

Salamander
Metal Slug
Outrun
Magical Drop 3

I just got Magical Drop 3 from BlueBMW recently. I've definitely played this in short half hour spurts. I change my answer. This is a great game!

[Desh]

I'll usually pop in Contra, Sunset Riders or Danny Sullivan.  If I'm really feeling froggy and want to take out aggression I'll pop in any Grand Theft Auto and just cause some mayhem.