Navigating the many versions of Cisco wireless software can become a headache. I often use the newest versions, especially when working with the latest Cisco APs (such as the new 2802i). This is not always practical or possible, especially when working in an existing environment where specific versions may be required for compatibility or stability reasons. The Cisco Wireless Solutions Software Compatibility Matrix has cross referenced lists of AP, WLC, MSE, Prime, and other related component versions.
Another helpful resource is the list of WLC versions supported by the TAC, along with brief notes on each.