If you're looking to kick off the week with a free game, Electronic Arts has the great tower defense epic Plants vs. Zombies Game of the Year Edition up for grabs on Origin.
Plants vs Zombies is a story about a horde of cartoonish undead with an unusual fixation on eating the brains of one particular suburban homeowner, who is protected from that grisly fate only by the plants in his garden. It's a bizarre setup but it works brilliantly, and despite its obviously casual, "games-for-kids" styling, it made a huge splash with mainstream gamers when it was new. It's now eight years old (kind of hard to believe) but remains, with all due respect to Bejeweled, Popcap's crowning achievement.
If you missed out on it, this is an easy opportunity to find out what all the fuss is about. Hit the On the House page on Origin, select "Add to Game Library," click the download button (assuming you want to try it out right away), dick around a bit with Origin's terrible folder management, and then finally you're off to the races. The whole thing is about a 200MB download, so schedule your time accordingly.
As usual with Origin's On the House program, there's no indication as to how long it will be free, but once you get it, it's yours to keep. And now, let this tunnel into your brain.