Recently one of my team member was in the midst of migrating to a new database and was performing some testing and encountered some problem. I told him to go back to the code and make the changes and testing. However, when he did that, he found that the person who previously wrote the code (and left the company) failed to checkin the source code into our SourceSafe repository.
As such, I went to search for decompilers. I came across many articles but the following are the more helpful ones:
Decompiling .Net Assemblies
For .Net, it appears that Reflector is the free solution recommended.
There were a couple of sharewares that did the samething - Spice, Dis# and Salamander.
For Java, you have Jode and Jad. Hmm, where do this people come up with these names :)