Those I know
- Wilderlands of High Fantasy (Judges Guild). The first setting I bought, the first I ran an OD&D game in and the first I ran a 3.5 D&D game in. I've used this and the City State of the Invincible Overlord since 1978. I was a pretty big fan of Judges Guild products in that period, even though I didn't buy that many of the detailed settings like Shield Maidens of Sea Rune until recently. I did buy Thieves of Fortress Badabaskor back then and even started doing a conversion of it to D&D3.5, but I'd now run it with Swords & Wizardry meaning a lot less work would be required.
- Glorantha (Chaosium/Issaries). After the Wilderlands another great setting, which I have a lot of affection for. Glorantha has now had the Second Age setting information released by Mongoose Publishing with their version of Runequest. The things that I like are the breaking with standard fantasy tropes like the elves being plants, dwarves being machine like and dragons as pretty much mythical creatures of immense power that PCs are unlikely to encounter except as a manifestation of a dreaming dragon. The depth of the mythology and its interaction with the land in Glorantha helps create a feeling of verisimilitude. I'd still tend to play using second edition RuneQuest, though I am keen to try HeroQuest at some point.
- Blackmoor. Dave Arneson's campaign setting that was originally published by Judges Guild and then had a more recent release for D&D3.5 from Zeitgeist Games. This is one of the classic old school settings for me with the mixture of humour and oddity from matching descriptions to physical models used to represent things and in jokes about other gamers that Arneson knew.
- Al-Qadim (TSR). One of the few TSR settings I had much liking for, finding a lot of the other ones a bit bland with the same old same old rehashed medieval Europe style. There are reservations I have about Al-Qadim, mainly shoehorning in all the standard D&D races, but I've always liked the flavour of the setting all the same. I'd probably play in it using houseruled Swords and Wizardry these days.
- Warhammer. Games Workshop's Warhammer world I like, but not uniformly as there have been better and worse takes on it over the different versions of the RPG and wargame. I like the Old World for its renaissance feel which is unlike the more mediaeval approach of most fantasy settings, the New World of Lustria contains my favourite Warhammer army the Lizardmen, but is a little cliched as impenetrable jungles. With the Lizardmen I like the Mayan/Aztec stylings adopted for their weapons and decoration. For roleplaying I think I'd stick to WFRP2 for rules at the moment, though with some houseruling as I'm reserving judgement on WFRP3.
I'll do a separate post about the ones that I'm interested in but don't have enough experience of to really comment.