I went to a St. Patrick's Day Party at a friend's house last year and was subjected to 76 different versions of Danny Boy. There were versions that took me to the edge (of tears), and versions that took me to the ledge, moments the song took me to Galway Bay, and others that felt more Guantanamo Bay. Overall, it was an interesting experiment and an excellent party gimmick.
If you'd like to create a comprehensive Danny Boy playlist, you can find a decent list of recordings of Danny Boy by notable artists on Wikipedia. My two favorite versions are by Sinéad O'Connor and Johnny Cash—both a little raw, world-weary, and sad. Other notable versions are by Christy Moore, Shane MacGowan, Judy Garland, and of course, Elvis, and I love a good instrumental version. Also, I can't believe I'm saying this, but I quite liked Michael McDonald's version on Natalie MacMaster's album.
I pulled together a playlist of thirty versions of Danny Boy (just the tip of the iceberg) on Amazon, if you'd like to be a one-trick-DJ at your St. Patrick's Day Party. Trust me, your friends will be talking about it for days, and singing about it for weeks!
And here's Sinéad O'Connor singing along to Davy Spillane's Uileann pipes (close your eyes to cheesy slideshow and just listen):