The Settlers II: http://www.gog.com/en/gamecard/the_settlers_2_gold_edition/
Patrician 3: http://www.gog.com/en/gamecard/patrician_3
Gothic 2: http://www.gog.com/en/gamecard/gothic_2_gold_edition
Space Quest 4-6: http://www.gog.com/en/gamecard/space_quest_4_5_6
King's Quest 4-6 http://www.gog.com/en/gamecard/king%E2%80%99s_quest_4_5_6
Gabriel Knight 1: http://www.gog.com/en/gamecard/gabriel_knight_sins_of_the_fathers
Broken Sword 2: http://www.gog.com/en/gamecard/broken_sword_2__the_smoking_mirror
BASS: http://www.gog.com/en/gamecard/beneath_a_steel_sky (it's freeware)
Runaway 1: http://www.gog.com/en/gamecard/runaway_a_road_adventure
TLJ: http://www.gog.com/en/gamecard/the_longest_journey
Simon 1: http://www.gog.com/en/gamecard/simon_the_sorcerer
Simon 2: http://www.gog.com/en/gamecard/simon_the_sorcerer_2
HoMM III: http://www.gog.com/en/gamecard/heroes_of_might_and_magic_3_complete_edition/
Freespace 2: http://www.gog.com/en/gamecard/freespace_2
BG&E: http://www.gog.com/en/gamecard/beyond_good_and_evil
JA 2: http://www.gog.com/en/gamecard/jagged_alliance_2
Earthworm Jim 1+2: http://www.gog.com/en/gamecard/earthworm_jim_1_2
(Full catalogue: http://www.gog.com/en/search/).
The legendary, beautiful game mentioned in Rubang's sig (I never finished it but I bet he did): http://www.anotherworld.fr/anotherworld_uk/
My No. 1 recommendation, though, will always and forever be my most favourite game of all time, MI1+2:
http://www.lucasarts.com/games/monkeyisland/
http://www.lucasarts.com/games/monkeyisland2/#/home (remake of MI2 not yet released)
Also, of course always good for a replay, the other brilliant ones besides Grim Fandango: The Curse of Monkey Island, Day of the Tentacle, Full Throttle, Sam & Max Hit the Road, Indiana Jones & the Fate of Atlantis (the latter one is on Steam).
Grim Fandango is good start and one of the best adventure games ever made, but does it work on modern systems? I haven't played it in at least 5 years. I hope GF will be LucasArts' next remake project (this game needs proper point&click controls).
Also, I wished I could still play Dungeon Keeper (1 or 2, doesn't matter, both were excellent)...
