Irish polkas are fun and exciting, but because they have less fast diddly notes than jigs and reels they are much much easier for beginners. Any polka you know or have a recording of will do, but make sure it's an Irish-style polka(they are not the same as ordinary polkas).. Or if you want to look in a book, I think Brid Cranitch's series " Irish Session Tunes" (there are various books in different colours) are very good. They come with a helpful recording.Ossian publications.