I have a Leopold with MX Browns at work. I works, and most importantly, the keys haven't started binding like the rubber dome Dell keyboards I had before it.
It's not as crisp as my Model M at home, and the pressure needed to actuate the keys is lighter. However, it's quieter, smaller, and it has a USB plug instead of PS/2. My work computer doesn't have a PS/2 port, which is why the USB plug is important.
I use the Type Heaven
. It's fairly quiet, and responsive enough to be satisfying.
I'd really like to try a Topre keyboard. The high-end Topre has keys that are weighted differently depending on how far away they are from the home row.