Hi Delenn,
There are so many good hidden object games around these days it would be hard to list a top five, though I would agree with Merri on Treasure Masters, I beta tested it so played out most of the levels and was always impressed by the innovations that I found; (most of which have since been copied elsewhere. Another I'd highly recommend is at least one of the Dream Chronicles games (there's two now, both of which are gorgeous and very playable). Hidden Expedition Everest was an early favorite. I'm sure Big Fish gave one away (either Everest or The Titanic). Another I enjoyed playing (and because I beta tested it played through almost to the end was Unicorn Castle, and finally Mystery Legends: Sleepy Hollow. I’ve included some you tube videos of the ones I’ve mentioned plus one for Berlin Nights as I’m thinking of getting it soon.
Treasure Masters:
http://www.youtube.com/watch?v=czJAd2R542g
http://www.youtube.com/watch?v=Hkx8DosP8yQ
Mystery of Unicorn Castle:
http://www.youtube.com/watch?v=szVI8JTrSz4
http://www.youtube.com/watch?v=y4HiwvE5QUs
Dream Chronicles
http://www.youtube.com/watch?v=AgW3tuiTo2U
http://www.youtube.com/watch?v=olM0YC3V-DM
Dream Chronicles 2:
http://www.youtube.com/watch?v=sEIu74xk_Fk
http://www.youtube.com/watch?v=dssYlUklBiM
Berlin Nights:
http://www.youtube.com/watch?v=ynto8CIipfQ
Mystery Legends: Sleepy Hollow:
http://www.youtube.com/watch?v=KLB67T_2nGc
http://www.youtube.com/watch?v=gwPcBXmsPPM