Music - Keyboard - Sharps and Flats

A black key to the right of a white key is called a #(sharp).

Black keys to the left of a white key are called a flat.

This is easy to remember because the left side of the keyboard is descending (Going down) and the right side is ascending (Going up), therefore the black keys to the left of a white key are on the 'descending side' and called a FLAT - kind of logical and easy to understand.

Check out this webpage, it has a good diagram explaining this: http://www.musictheory.halifax.ns.ca/3keyboard.html