Since you've arrived here you probably know what brainf*** is. If not then you can find out more at http://home.wxs.nl/~faase009/Ha_BF.html or http://www.muppetlabs.com/~breadbox/bf/.
Brain Strain is a Windows debugger for brainf***. Amongst other things it features chromacoding (aka syntax highlighting) of your brainf*** source code, single stepping, breakpoints, code animation and a memory monitor.
Brain Strain is open source software, it's free and it's licensed under the GPL. You can download the latest binary and source distributions from the Project Page. You can also use CVS to check out the source code.