I've really gotten into using digital images on my cards. They're clean and simple, but there are some tricks I'd like to learn to complement the illustrations I use. I tried using "Gimp for Dummies", but it was too hard (yes, I know how bad that sounds).
Anyway, one of my favorite illustrators is Jessica Weible, who I found on Etsy. Here are some of the cards I've made using her designs:
She has other great designs on her website jessicaweible.com. Here are just a couple: