I found this great old book about Welsh fairy lore called "British Goblins Welsh Folk-lore, Fairy Mythology, Legends and Traditions" by Wirt Sikes. It has the names of the different types of Welsh faeries, and detailed info about what they do. The book was written in 1870, so it comes after the British government tried to stamp out Welsh langage and culture, but the author talks with older people who already knew the old stories and traditions.
You can find various free versions online. I found a free Kindle ebook of it:
http://www.amazon.com/British-Folk-lore-M ythology-Traditions-ebook/dp/B004UJCH80
Source:
http://nonwiccanwitch.livejournal.com/400114.html