Engagement Party Ideas?

My FH and I are planning on having an engagement party during the summer- a backyard party at my mom's house.

I already have ideas for the wedding to possibly do a wish tree, candy or cookie buffet, fun guest book with polaroids ...what are some fun things I can do for an Engagement party to make it more memorable and unique? I was thinking of stringing a clothes line with pictures which I think would be a neat touch.
Any other fun ideas/activities/special touches would be great :)

I think the clothes line idea with pictures is a great idea...it's a great way to display pictures of you and your FH as kids and now.

If your backyard has trees, putting up lighted lanterns would be pretty at night.

I am also having an engagement party in the summer so, I will keep thinking of more ideas...

Thanks for your idea tbmaz!
I will definitely be hanging lights....maybe out of jelly jars? There are a lot of ideas on Martha Stewart's website for that. Also, I might make a ton of those inexpensive poms out of tissue paper. I've seen them on a lot of wedding blogs and they're just so darling and a big bang for the buck.

Keep the ideas coming