All packs on sale: http://store.steampowered.com/search/?sort_by...egory1=996

All id games for $30: http://store.steampowered.com/sub/440/

All unreal games for $25: http://store.steampowered.com/sub/683/

All painkiller games for $15: http://store.steampowered.com/sub/8684/

Valve pack for $50: http://store.steampowered.com/sub/7930/

Just about everything is on sale to some degree. Full list here.