Filtered (by filetype) search of files.
For instance, 'pdf resume' will return all *.pdf files containing 'resume'; 'doc report' all *.doc, *.docx, and *.pages containing 'report', etc (see screenshot below).
All workflows are based on Vero Pepperrell's PDF File Searcher, are easily modifiable to get a filtered search for any filetype, and can be downloaded here:
http://koniev.com/alfred
P.S. There is probably another way to do this kind of filetype search with Alfred. If so, let me know.