My friend had a giant colouring in painting made for her wedding. We all got to colour it in with paint pens and made a piece of art. It was totally personalised and really well made. It was such a talking point and got everyone chatting. They now have the finished product up in their living room. Definitely the most unique fun thing I've seen at a wedding so far!
Photobooths are always fun but they seem to be at every wedding now. Garden games are fun too if you get the weather for it!
Go for a dress-up box near the corner of the dancefloor. Silly wigs, glasses and masks etc.
Really funny and all our guests got into the spirit and partied with them!