For the more adventurous and cost conscious ...
For those of you who are a bit more adventurous and cost conscious, there are open source programs that can perform digital room correction using a PC that are available on SourceForge:
DRC: Digital Room Correction
Convolver — a convolution plug-in
The first program linked will generate digital FIR filters based on room response measurements. The second link is to a convolution program which will implement FIR filters in real time as a DSP plugin to Windows Media Player.
Obviously, these programs are likely not to be as polished or user friendly as commercial products, but that is not always the case. However, for the technically inclined, it is quite possible that they may have greater functionality and flexibility.
I have not tried any of this myself yet, but I have wanted to for a number of years and I would love to hear about anyone who does try it and what kind of results they were able to get. It has always seemed like a fun audio DIY project.
David