I'm with everyone else - I use all kinds of random things!
I dunno if anyone has mentioned felties - I don't make mine but you can buy them reasonably priced. I do make felt centers, usually hand-cut and embroidered, but that's one of my specialties
Faux flowers, feathers, fabric covered buttons, rhinestones, resins (check out hairbowcenter.com for a good selection and low pricing)...I have even used paper flowers as embellishments! Anything goes