The Fabco NV-55 is a decent needle valve. There are some good metering valves that Swagelok and Parker make as well, and you can sometimes find excellent deals on these metering valves on eBay and/or the Swap and Shop subsection of these forums.
For some more information regarding needle/metering valves, please take a look a the pressurized CO2 article that I have written (it is linked in my signature).