In MFDiff, at least when launched from Slickedit, add context menus for file-exclusion.
For example in ProcMon, right-click on a log entry and there are a variety of include/exclude options.
If I diff two folders and I find there are a bunch of *.txt files that I don't care about, I could simply right-click one of them and have options like:
Exclude: *.txt
Exclude: ThisFile.*
Exclude: ThisFile.txt
Exclude: C:\This\Entire\Path\
Exclude: C:\This\Entire\Path\*.txt
Exclude: C:\This\Entire\Path\ThisFile.*
Exclude: C:\This\Entire\Path\ThisFile.txt
Copy: ThisFile.txt
Copy: C:\This\Entire\Path\ThisFile.txt