We were recently in charge of invitations for a baby shower and had grand ambitions of designing them from scratch. Being neither particularly design-savvy nor an expert in Illustrator, we gave up after a few hours and instead went with a fill-in invite that was beautiful, but on the expensive side. We wish we'd known about Silhouette Blue at the time which has some great designs that won't break the bank.
Silhouette Blue is the work of Megan Nutley who creates and assembles her stationery by hand outside of Chicago. Many of her designs are geared toward children and babies, but there are also adult options for birthdays, moving, congratulations, bridal showers, etc.
Fill-in invitations, like the hula girl and cowboy above, have space on the back for all the party details and sell for between $11 - $12.50 for a set of 8. If you don't want to handwrite them, you can easily set them up for imprinting on your computer.
She has a few options specifically for baby showers which come in green, pink, blue and orange.
We're also big fans of these personalized notecards ($25 for 20) which your kids can use for thank you notes or to go old skool with a snail mail letter to grandma.