Thin Lizzy's Whiskey in the Jar is great, though I also have a soft spot for the Metallica version. Which I suppose counts as a cover even though it's a traditional song, as they would never have thought of recording it if Lynott and co. hadn't been there first.

Lynott's more mournful voice makes more sense in the context, but I do like the oomph of Metallica's take.