Eladrin
Much of the following is taken from the Wikipedia page on Eladrin, as they are very scattered in appearances.
2e
- Planescape: Monstrous Compendium Appendix II
- Warriors of Heaven (first appearance as a playable race)
3e
- Monster Manual (Under celestial)
- Manual of the Planes (again under celestial)
- Savage Species (as a race and playable class)
3.5e
- Monster Manual (revised edition)
- Book of Exalted Deeds (also features the Court of Stars, paragons and other key beings)
- Fiendish Codex I: Heroes of the Abyss (details the role in the tanar'ri uprising)
4e
- Player's Handbook (Core race living in the Feywild)
- Monster Manual
- Forgotten Realms Player's Guide (moves moon/sun elves as subgroups of Eladrin)
- Heroes of the Fallen Lands (again as a core group)
- Player's Handbook II (paragon path), Monster Manual II, Martial Power (paragon path)
5e
- Dungeon Master's Guide (as subrace of elves)
- Mordenkainen's Tome of Foes
Feywild
- Manual of the Planes (4e) - General characteristics, ways of transition from the Prime world and back, inhabitants, significant places.
- Player's Option: Heroes of the Feywild (4e) - Presents history, stories, settings, player races and subraces, adventure hooks and options.
- Beyond the Crystal Cave (4e) - Adventure module from Season 7 of D&D Encounters, not a sourcebook but does detail the feywild and has interactions with inhabitants
- Complete Guide to Fey (3.5e 3rd party book) - Rules for Fey hosts, courts, cycles, player races, creation of new fey races. Attempts to be a complete fey sourcebook for the 3.5e system.
- The Feywild (5e DM's Guild release) - Lore, history, maps, locations along with rules for subclassing, crafting and several new monsters and magic items.