h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Don't forget Northern Ireland! One that always trips people up is Ahoghill, as of course everyone insists on saying A-hog-hill. In fact it's a-hoch-ill ('hoch' rhymes with Scottish 'loch' and has the same soft 'ch'). The overall effect is of someone trying to clear something stuck in their throat.

I reckon someone needs to collate the Irish ones for a sister article. Post them here and maybe someone will pick it up. RoI too.

Icy

Well, there's the town of At Henry, from the well-known song.

TRiG.

'Cause Athenry's not in the North.

Mostly, I think you should be OK in Ireland if you remember that 'ch' and 'gh' both take a soft 'ch': eg. Drumballydonaghy isn't pronounced 'donagy' but 'donahy'.
Also, remember that in Gaelic, 'bh' is pronounced 'v': hence in Cork, Cobh is pronounced 'Cove'.

I remember a heated argument breaking out on a family holiday to Galway on the pronunciation of Tuam (Tu-am? Chu-am?) In the end we had to stop the car when we reached the town and ask a friendly local. Turns out you say it 'Choom'.
Also in Galway, the longest place name in Ireland, and (allegedly) the longest port name in the world: Muckanaghederdauhaulia, which is chock-full of potential pitfalls, mostly revolving around the two 'd's. It goes something like: 'Mwig-unnok-ither-gaw-hawl-ya'.

Some names that are pretty pronounceable but mildly amusing are Sneem, Cong, Spiddal, Bruff and Furbo. I also like Two-Mile Borris.

Enlish visitors always think we live in TULL-a-more. We don't. It's Tull-a-MORE. So there!

TRiG.