Beyond the benefit of having onesies that your close friends and family have made for you, it can also be a cost-effective way to add some cute bodysuits to baby's wardrobe.
Being a DIY crafter, I'm always inclined to check out what ETSY's offering. (Not only are you supporting independent artists, but you can find stuff that isn't on the commercial market.)
I found quite a few cuties!
(This one's from O'Dell Sisters, $16)
(This one is made by Sue Czechowski, $12)
(This one's from SwankyShank, $18)
(Cute tuxedo onesie from Lil Ladies and Gentlemen, $22)
(Paisley Prints Spokane, $19.95)
(So cute! From The African Llama, $20)
(The Lil Nest, $25)
Buying these individually can add up quickly, but finding cute ideas like these and making them yourself (or offering them as ideas at your own onesie decorating party!) is a great alternative!
In addition to providing puff paints and markers, I suggest bringing fabrics as well. This way, guests can cut out shapes and designs. (You'll probably also need fabric glue, buttons, thread and needles and other cute little details!)
This pic from Pizzazzerie is exactly what I'm talking about...