J.B.
When my grandparents celebrated their 50th their children also hosted a big party like you're planning. We (the grandchildren) had a large gold-tone platter made that listed their names, wedding date, anniversary date, and something like "with love from your Grandchildren" and then listed all 15 of our names. It was something that they proudly displayed in their dining room and looked pretty among their most special dishes and glassware.
Another idea that I really, really love is puzzle piece picture frames...you can personalize these and put in photos of their wedding, you kids, their grandchildren and leave a spot open for an anniversary photo. The big piece that goes in the middle would be a perfect place to put a wedding photo and then later a photo from their party when they're all dressed up and photo ready:
http://www.personalcreations.com/puzzleoflife?productgrou...
Congrats to your parents and have fun planning!
ETA based on Diane B.'s answer - we also had the privilege of seeing both my grandmother and my husband's grandmother reach their 90th birthdays. For each, we did digital scrapbooks from either Shutterfly or Snapfish where I had everyone send me photos (either snail mail or via e-mail) and I scanned all of the physical photos (which took forever) and uploaded the digital ones. Once they were all uploaded, I created big photo books using the colorful templates that these services have and then had the books printed with embossed leather covers. So if you're not into paper crafts (which are awesome but can be really time consuming) then you can have gorgeous photo books made on-line. It still takes a lot of time, but you don't need to buy papers, scissors, stickers, glue dots, etc.
And yes on the video idea! My FIL put together a video for his mom's 90th birthday where he interviewed family and friends about her (and her husband, who had already passed away) and then interviewed her as well. How fun would it be to get your parents together on video talking about how they met, funny stories from when they were newlyweds, etc? Then someone in the family edited the clips together, added in some transition slides introducing the next clip, etc. They showed it at her party and it was HUGE hit. But we didn't really know the value of it until she passed away this past fall at the age of 94. We played the video at a luncheon after the funeral and it was really special to have her voice and her words and her mannerisms captured for us to remember.