The scalloped circles I use on many of my cards are some of my favorite shapes to use in cardmaking. The style really dresses up a card without too much effort. Sometimes I use the Marvy punches (Mega and Giga sizes - the pink and purple ones), and sometimes I use the Nestabilities dies in my Cuttlebug machine. Overall, I prefer the Nestabilities because there are more sizes of the die available which means that you can customize what size of circle you want to cut in relation to the stamped image. I have seen the Marvy punches in Michael's and JoAnn's, but to be honest the supply doesn't seem to be very consistent so it often depends on sheer luck as to whether or not the punches will be in stock. Here is a link to an online seller of the punches, and here's one place where you can check out the Nestabilities dies.
On one of my recent TCP Tuesday cards (I've posted it again here on the left for you to see), I used a scalloped circle and then used a plain hand punch to add punched holes around the edge. I really like the effect it made!
Another question that has come up is about my coloring materials. The images that you see colored more boldly on my cards are most likely colored with my Copic markers that I got through My Favorite Things; I also like the PrismaColor markers (PrismaColors can be picked up individually or in sets at Michael's - a great deal with a coupon!).
I also use a technique with regular colored pencils (not watercolor ones), Gamsol (a.k.a. odorless mineral spirits) and blending stumps. I found out about this technique from a tutorial by Cecilia Ross on Splitcoast Stampers - here's a link for you to check it out since it explains the process way better than I could! I love the style of this method: it's a little bolder than watercoloring, but not as intense as the markers.
Have fun! I hope this information helps!
ETA: you can find the Odorless Mineral Spirits at Michael's near the artists' paints: it is made by a brand called Mona Lisa. Happy shopping!