No particular order:

1) Planescape Torment - PC (quite possibly the greatest RPG ever made)

2) Shadowrun - SNES (the world and story were like nothing ive ever played before)

3) Chrono Trigger - SNES (some of the most memorable character design and gameplay)

4) Diablo 2 - PC (i know, i know but it IS an action rpg. and maybe the most addicting game ever made)

5) Final Fantasy 4 - SNES (the greatest characters and story EVER told in a video game)


honorable mention: Legend of Zelda the Ocarina of Time...
though depending on who you ask, Zelda is an adventure game