All pronunciations are given phonetically. This only covers races explicitly named in the first six books, omitting Undersea races not appearing in, or mentioned in, book six.
Afanc: ah-fank. Plural is Afanc.
Annwn: ah-noon. No plural exists.
Bannick: ban-nick. Plural is Bannicks.
Barghest: bar-guy-st. Plural is Barghests.
Blodynbryd: blow-din-brid. Plural is Blodynbryds.
Cait Sidhe: kay-th shee. Plural is Cait Sidhe.
Candela: can-dee-la. Plural is Candela.
Coblynau: cob-lee-now. Plural is Coblynau.
Daoine Sidhe: doon-ya shee. Plural is Daoine Sidhe, diminutive is Daoine.
Djinn: jin. Plural is Djinn.
Dóchas Sidhe: doe-sh-as shee. Plural is Dóchas Sidhe.
Ellyllon: el-lee-lawn. Plural is Ellyllons.
Gean-Cannah: gee-ann can-na. Plural is Gean-Cannah.
Glastig: glass-tig. Plural is Glastigs.
Gwragen: guh-war-a-gen. Plural is Gwragen.
Hamadryad: ha-ma-dry-add. Plural is Hamadryads.
Hippocampus: hip-po-cam-pus. Plural is Hippocampi.
Kelpie: kel-pee. Plural is Kelpies.
Kitsune: kit-soo-nay. Plural is Kitsune.
Lamia: lay-me-a. Plural is Lamia.
The Luidaeg: the lou-sha-k. No plural exists.
Manticore: man-tee-core. Plural is Manticores.
Naiad: nigh-add. Plural is Naiads.
Nixie: nix-ee. Plural is Nixen.
Peri: pear-ee. Plural is Peri.
Piskie: piss-key. Plural is Piskies.
Pixie: pix-ee. Plural is Pixies.
Puca: puh-ca. Plural is Pucas.
Roane: row-n. Plural is Roane.
Satyr: say-tur. Plural is Satyrs.
Selkie: sell-key. Plural is Selkies.
Shyi Shuai: shh-yee shh-why. Plural is Shyi Shuai.
Silene: sigh-lean. Plural is Silene.
Tuatha de Dannan: tootha day danan. Plural is Tuatha de Dannan, diminutive is Tuatha.
Tylwyth Teg: till-with teeg. Plural is Tylwyth Teg, diminutive is Tylwyth.
Undine: un-deen. Plural is Undine.
Urisk: you-risk. Plural is Urisk.