Sure, you can use Onyx or Terminal and do some command line work. But it's much easier to drop into Dashboard, hit "Show" on the blue button and have Finder relaunch, showing all invisible files. I had to click on Finder in the Dock to actually launch it again, but when I did there were those lovely .DS_Store files, staring me down. I use this to remove the hidden _files off my daughter's PC-friendly MP3 player. That way she doesn't have to scroll through resource-fork versions of her songs.
The widget is free and available from developer Matthew Hansen's page.