Here's a comparison chart. There are a couple things missing in the express version that might matter to someone:

http://community.sharpdevelop.net/blogs/mattward/archive/2006/07/12/VisualStudioExpressComparison.aspx

>Considering that Visual Studio Express is free, I dunno why someone would use a different IDE.
>
>>Although, technically one could also use the free IDE CsharpDevelop (I believe it's called). I used it a couple yrs ago and it was maybe 80% of what VS IDE provided.