I can find all sorts of alphabet flashcards at the dollar store, but 99% of them have both the upper and lower case letters together. Most of my students can recognize the upper case letters, but have difficulty with the lower case ones.
Enter Worksheetworks dot com and Alphaflash. This website is fantastic! You can print out your own cards, in varying sizes and fonts, with just the upper, just the lower, or paired letters!
Since I save "gently used" colored cardstock (which has been printed on one side only), I can run off as many sets as I want. This allows me to have different colors for different purposes: ex: blue for a matching memory game, yellow for flashcarding, etc.
In case you lose it, I'm adding the site to the sidebar of this blog.