I find it often difficult to find the right buttons for my needlework. At Univers du crochet d’art I eventually found an instruction on how to crochet (and embroider) buttons. It is written in French, but the tutorial is illustrated so that I could easily understand what to do.
On the photo you see my self-made button, it is worked in crochet and then embellished with embroidery.
Addendum of June 23, 2010: The Univers du crochet d’art moved and I didn’t find the instruction there and nowhere else in internet.
But there are many instructions for crocheted buttons, you simply have to choose another one ;-)
Links:
Univers du crochet d’art: A french website on crochet
Page moved to: A french website on crochet
Crocheted buttons (French) (with explaining pictures)
The link doesn’t work anymore, try the Google search result for ‘crochet button’