Looking on a few different sites this list seems to have everyone that attended. It wasn't a very extensive guest list, with only 10 fellow Game of Thrones actors attending, and a rather dull wedding since no deaths were reported either.
Emilia Clarke (Daenerys Targaryen).
Sophie Turner (Sansa Stark) and Maisie Williams (Arya Stark).
Liam Cunningham (Davos Seaworth).
Richard Madden (Robb Stark).
Peter Dinklage (Tyrion Lannister).
Ben Crompton (Dolorous Edd).
Conleth Hill (Varys), John Bradley (Samwell Tarly) and Joe Dempsie (Gendry).