http://www.basilwhite.com/sudokusolver.pdf - Adobe Acrobat format. Easiest to scale to fit your paper or card.
http://basilwhite.com/indexcardsudoku.gif - GIF image.
http://basilwhite.com/indexcardsudoku.doc - MS Word.
http://basilwhite.com/indexcardsudoku.psd - Photoshop.