If anybody can recommend a nice command-shell (or toolpack) that supports the standard unix commands (grep, cat,...) for windows, my ears are opened wide

I'd just like to have a little shell that allows me to sniff a bit around with standard-unix-commands and maybe solve some occasional tasks using them, so it's mainly out of curiosity. I didn't find a suitable shell yet after a little research, so if you can recommend one, don't hesitate to let me know...