Go to www.ti.com, under microcontrollers at the left panel.->Getting Started->Free Software Downloads underneath the page.
There are several options. IAR kickstart and Code composer.
IAR kickstart description: 4K C-Compiler/Assembler/Debugger/Simulator. Use this file only to install the most current Embedded Workbench Version 3 Kickstart system.
Code composer: Fully Integrated MSP430 Development Environment with up to 8K Bytes Code Space.
Code Composer Essentials (CCEssentials) is a powerful and easy-to-use integrated programming and debugging environment for the industry-leading MSP430 ultra-low power microcontrollers.
The full version of code composer seems to be a lot more cheaper than the full version of IAR, i think.
Code composer based on Eclipse IDE while IAR has its own IDE and debugger interface