It's Rockstar Week on Steam, which means there are an abundance of discounts to be had! For the next 3 hours, Grand Theft Auto IV is on sale for $7.50 USD, and the entirety of the Rockstar collection is up for 50% off ($42.49 USD instead of $84.99 USD). (More discounts will follow.)
A complete listing of the games included in the Rockstar Collection package can be found on the Steam website. Don't forget to join the Rockstar Games Official Group on the Steam Community to receive up-to-date alerts whenever new discounts are announced.
Note: Apparently the discounts on individual titles aren't available in Europe, however the 50% discount on the Rockstar collection is available.
Rockstar Discount Week on Steam - Shack News
Rockstar Collection package on Steam