A couple of years ago, we threw a Halloween party for my daughter and a bunch of her friends. It was the first year that my daughter was too old to go trick or treating. (I know, I know. We still have old teenagers coming around every Halloween, too. But we just decided that at 13, it was time to do something different.)
We decorated outside the house with "monster foot prints" leading up to our house. We simply used sidewalk chalk to make the monster prints. Easy and the kids did it all on their own.
We also made tombstones with funny sayings. I just took old moving boxes (you know we always have lots of those around with as many moves as we've made) and cut them into tombstone shapes. We painted them grey by mixing left-over black and white craft paint. After that dried, I wrote names on the tombstones with Sharpie marker.
I let the kids pick the names from a list we'd come up with ourselves plus a quick internet search. The tombstones were a big hit with the girls coming to the party and with the trick or treaters. My favorite? I'm glad you asked. Lee Ning with the tombstone leaning, still makes me laugh. The kids' favorite? Seymore Butz. Yeah, yeah, they were 6-13 years old then.
The best part of all - the decorations were free and a fun project that the whole family did together.