Geos Image Editor by David Lee - I saw this cool utility for Windows posted on Facebook the other day, and have to share it because anyone that programs for GEOS needs this in their toolbox.  Here is a quote from the author about the utility:

Utility for creating bitmaps for geos programming. Left click and move mouse to set; right click and move mouse to clear. Click the 'Get Assembly' button to display window that has ".byte" statements for geoProgrammer and many cross assemblers; "b" statements for MegaAssembler; and a "c" string suitable for cc65. Copy the desired format and paste into source code.

I know it sounds simple, and it is!  That's the beauty of it.  No need to install, just extract it to a folder and run the executable.