The Steam Summer Sale has begun, with the customary massive discounts off of a huge range of games. As is typical for the Steam sales you'll see a number of older games that have been on sale before (such as Half-Life 2 which pops up each time) but there are new titles as well such as the PC release of Dead Rising 3 with 25% off before it's even released.
The Steam sales usually have a gimmick attached to them and this one is no different, with the Summer Adventure. As with previous sales, you can collect trading cards and collecting the full set of trading cards will let you craft the Summer Adventure Badge.
When you craft the badge you can join a random team of other Steam users, with the teams competing to make the most points each day and thirty members from the winning team will will three games off their wishlist, so make sure that you have games that you want on there in case you're one of the lucky ones!
The usual Steam buying logic still applies, and I'd recommend not buying things unless they're on a flash or daily sale or the community choice game, as you'll almost certainly be able to get it cheaper later on.