Mac OS X
Installation using Fink
Fink provides the complete MSP430 toolchain including mspdebug for 10.4-10.7 (but only tested on 10.6 & 10.7)
Packages are listed here, and were shepherded by Matthias Ringwald.
If you don't use Fink yet, please follow the Installation from Source Guide.
Then, you can install the toolchain with
"fink install msp430-libc msp430mcu mspdebug"
Most parts of the toolchain will end up in /sw/lib/msp430/
Installation using MacPorts
The complete toolchain is available on MacPorts. You can find the packages list here. They are currently maintained by g5pw.
You can install the LTS version by typing
"sudo port install msp430-libc msp430-gdb"
or, if you want the latest version, just type
"sudo port install msp430-libc-devel msp430-gdb-devel"
TUSB3410 USB-to-UART drivers
Most TI programming devices and developer boards make use of the TUSB3410 USB-to-UART chip instead of actual USB communications. For more info, have a look at the sales pitch.
TI provides "unsupported"/3rd party  drivers for this chip. However, they don't contain all product IDs, follow the comments on the TI community page. The driver basically works, but it occasionally crashes which also seems to kill the whole USB subsystem, so you cannot type or move the mouse anymore. If you suddenly get errors in the mspdebug console, I recommend to open another terminal and reload the TI3410 kernel extension, re-plug the cable, quit mspdebug and start it again. I didn't had a crash with that procedure yet. Also note, that my system ALWAYS crashes if I try to use two TUSB3410 devices at the same time.
To reload the kernel extension you can use: "sudo kextunload /System/Library/Extensions/TIVCPSerial.kext/ && sudo kextload /System/Library/Extensions/TIVCPSerial.kext/"