Figured I would post a few.

[RevRagnarok]

If I have a lot in my download tab and want to percolate certain files to the top, I use this expression:

\.par|nfo|gif|jpe?g|\.txt

Then just click "FIND" and "TOP"

However, on my scratch list I wouldn't want that because I don't want to download all the par2 files by accident. For that, you use a negative look-behind:

(?<!\d)\.par|nfo|gif|jpe?g|\.txt

Which matches all the base par2 files but not the fill files (unless the base for some reason has a number there, you can't win them all!)