It's been a busy week for the stock market, most of it bad. Thankfully the folks at Valve know that everyone appreciates a sale and this weekend's game on sale via Steam is the original Peggle title from Popcap. The casual arcade game is normally $9.99 but you can grab it for just $4.99 this weekend. The sequel, Peggle Nights, will be released on Steam on Oct. 15

That's not all that's gone on at Steam, however. The download service just added a number of older Ubisoft games to its line-up, including both expansion packs for Heroes of Might and Magic V, The Settlers: Rise of an Empire Gold Edition, The Sum of All Fears and Brain Spa. All of these games are 10 percent off their normal prices on Steam until Oct. 17. You can also pre-order Far Cry 2 via Steam and get $5 off its normal price until its release on Oct. 22.

You want more? How about that World of Goo, the award winning indepdent puzzle/construction game from the two man dev team called 2D Boy, will make its worldwide debut via Steam Oct. 13? Pre-orders for the game are being taken for $19.99 and the Steam version will contain achievements via Steamworks. Finally, pre-orders are being taken for Egosoft's X3: Terran Conflict, the space trading-combat game. The release has now been confirmed for Oct. 17.