Mumford and Sons are terrific. I started listening to them a couple months back and they still get the most play on my IPod. As for some good Irish music I would recommend Greenland Whalefishers. The lead singer sounds almost exactly like Shane MacGowan in his better years. The Tossers are another great band probably my favorite Irish folk group at the moment. They hail from Chicago and write some of their own stuff along with some traditional Irish songs and they're hard to beat instrumentally. I would also recommend The Cherry Cokes if you have an open mind. They're actually from Japan but they handle a tin whistle and mandolin with the best of them. The lead singer has a bit more of a punk edge to his voice but they're good fun for a night of drinking.
I'm highly gratified that people keep coming back here and posting new things every once in a while. I really enjoy the exposure I get by all of your recommendations. Keep them coming!