DND_Reborn
The High Aldwin
Wow, there are so many products I never used but mostly because I didn't own them! 
I played Immortal Rules for nearly a year. It was incredible, but strange I must admit. We were in high school then.
I use 3E Oriental Adventures extensively and most of my 3E experience was with it. That campaign ran about 18 months-lots of fun.
Used Wilderness Survival Guide quite a bit, actually wrote an encounter/weather generator program based on the rules in it and adapted a lot of rules from it.
Used Dungeoneers Survival Guide but not as much.
Used most of the Guides and Handbooks from 2E at one point or another.
I think the only thing I remember having that I never used was HollowWorld (don't even remember if it was one word or two LOL!).

I played Immortal Rules for nearly a year. It was incredible, but strange I must admit. We were in high school then.
I use 3E Oriental Adventures extensively and most of my 3E experience was with it. That campaign ran about 18 months-lots of fun.
Used Wilderness Survival Guide quite a bit, actually wrote an encounter/weather generator program based on the rules in it and adapted a lot of rules from it.
Used Dungeoneers Survival Guide but not as much.
Used most of the Guides and Handbooks from 2E at one point or another.
I think the only thing I remember having that I never used was HollowWorld (don't even remember if it was one word or two LOL!).