A very funny "Over the Hill" invitation are these magazine cover invitations. Whether it's "Outta Time," "Hot Flash" or "Old Men's Journal," everyone will be roaring with laughter when they get them in the mail!
"This is your Life" Have family tell stories from the early years (a very long time ago), and grab a life-long friend or a teacher for the school years. A co-worker can recount famous (or infamous) moments at the office. You get the idea. Put together a CD with pictures from the corresponding years, and this can be a really fun hour or so. This approach can, and should, be funny, but it also lends itself to many touching moments and memories.
Rent a Hearse (amazingly this isn't that hard to do) and tour some of the old neighborhood hangouts. This is a blast, and provides fabulous photo opportunities.
The guests and the guest of honor will have so much fun they will eagerly await your next party!