Gamehouse http://www.gamehouse.com/ give away a free* game each day and a fair proportion of them are hidden objects (e.g. the current one Angela Young's Dream Adventure).
You just have to register on the site (I've been there for months without any problems such as spamming).
*It's free if you don't mind putting up with adverts; these seem to have become more frequent in recent times and appear every few minutes during gameplay. Otherwise you can get a pass for a monthly fee.