I made my in-law's a "surprise" quilt for their 50th. Now, bear in mind, I was involved in the planning of the party so I had a year in advance to prepare.
I chose this block (based on # of invitations sent out)
http://www.quilterscache.com/A/AmericanChainBlock.html
I mailed each person/family who was invited, the middle piece of fabric. I ironed each to freezer paper and instructed them to write their sentiments or simply sign, IN PENCIL. I used embroiderly floss to embroider their names/messages. I varied my floss to match the colors I had chosen for the blocks--lavendars/florals/ and greens.
Then, I assembled the quilt, bound it, quilted it and had it hanging at the cake table.
If you are not up for pre-mailing, you could construct a quilt, get some Pigman pens, and just have everyone who attends, sign a square.
After I finished the quilt, my MIL's 2 best friends both succumbed to cancer. She was really touched to see the messages they had written to her, in their own handwriting. It really was special.
HTH,
Julie