Dragon Warrior 4/Dragon Quest 4 is my favorite NES game soundtrack of all time. For a game like that to cram so much expression into its music absolutely floored me when I was younger. I was so disappointed when the US release for the Playstation remake of DQ4 was canned, but I bought the soundtrack as soon as it came out. Listening to the updated versions of the songs I loved was an amazing experience. The DS version is fantastic as well, and definitely worth checking out, although I am disappointed that the US release was missing content that was in the JP version.
Final Fantasy VI and Chrono Trigger are my favorite SNES soundtracks, and cover the majority of the songs I will randomly start humming to myself on a daily basis.
I also love the Estpolis/Lufia series' music. Very, very catchy stuff in there. As soon as I saw they were reprinting the "Biography" soundtrack collection a couple years back, I jumped on that so quickly!
Masqued Ferret - loved the soundtrack to Super Mario RPG!! Yoko Shimomura is one of my favorite game composers, and she really did a great job with that one.
Ceonn - I need to revisit Tales of Phantasia at some point, but you're right, that is a VERY good tune - tons of the Tales music is just phenomenal. Motoi Sakuraba is another one of my favorite game composers.