Oh, so YOU'RE the one person who hasn't played Plants Versus Zombies yet? Well, I guess that Steam has put it on sale at $3.40 just for YOU. Be polite and go buy a copy of it from them. Everyone else, take a look at Steam's other sale. Today only you can get several Need For Speed games at big discounts, NFS: Hot Pursuit is $14.99, Shift is $6.80, and Undercover is a mere $2.50.
Elsewhere, ImpulseDriven.com will let you buy TV Manager 2: Premium Edition for 75% off at $7.49... if that's the sort of thing you actually want to buy.
GamersGate.com has three Tomb Raider games on sale for around six bucks each, but they're also selling 87 other games at various prices as well.
Direct2Drive.com is running a Capcom Week and has nine games marked down by half. They include Dead Rising 2, Resident Evil 5, and Street Fighter IV among others.
Normally Direct2Drive.com has a bunch of mediocre casual games on sale for Two-Dollar Tuesday. Not today! Today they have the awesome indie game Braid for two dollars, along with a couple of mediocre casual games. Braid at two dollars is definitely our BEST DEAL OF THE DAY.