Delivery times may vary, I noticed on GTA it said usually ships within a month. Assassins Creed and Mafia 2 are both pre orders for release as part of the "Classic" or "Platinum" collection on the 17th and 10th of June respectively.
GTA
360 - http://www.zavvi.com/games/platforms/xbox-360/grand-theft-au…
PS3 - http://www.zavvi.com/games/platforms/ps3/grand-theft-auto-iv…
Assassins Creed Brotherhood
360 - http://www.zavvi.com/games/platforms/xbox-360/assassin-s-cre…
PS3 - http://www.zavvi.com/games/platforms/ps3/assassin-s-creed-br…
Mafia 2
360 - http://www.zavvi.com/games/platforms/xbox-360/mafia-2-direct…
PS3 - http://www.zavvi.com/games/platforms/ps3/mafia-2-directors-c…
That's not GTA IV Complete - that's just the Episodes.