Here's a collection of stuff I've built up from my daily job tasks. Probably nothing real astonishing, but they might be useful if you can't or are too lazy to figure them out yourself.

Mouse Wheel emulation
My wife wanted her Logitech TrackMan Marble FX's Little Red Button to work as it does in Windows. That would mean that whenever the button is pressed, the window scrolls with mouse movement. I found the trick on a newsgroup:
In /etc/X11/XF86Config (or wherever is appropriate for your system)
   Section "InputDevice"
        Identifier  "Mouse0"
        Driver      "mouse"
        Option      "Protocol" "MouseManPlusPS/2"
        Option      "Device" "/dev/psaux"
        Option      "Buttons" "4"
        Option      "Emulate3Buttons" "no"
        Option       "YAxisMapping" "4 5"
        Option       "XAxisMapping" "6 7"
        Option       "EmulateWheel" "1"
        Option       "EmulateWheelButton" "4"
File type conversion
This is a bash command line to convert PDFs to PSs. Presumably one could use this for any conversion utility requiring input AND output file names.
for i in `ls *.pdf | cut -d. -f1`; do pdf2ps $i'.pdf' $i'.ps'; done
Multiple file compression
I have a directory tree full of old log files that I keep individually gzipped. Since the logs come by mail there's no way to compress them as they come in. Here's a one-liners that finds and gzips anything that isn't already.
find . -type f -not -name "*\.gz" -exec gzip -9v {} \;
Copying a directory tree
If you're not lucky enough to be using GNU cp (with the -R option), the next best thing is tar. I didn't come up with this one, and in fact this exact syntax is out of a shell scripting class. I figure that just about everyone has seen this before, but it's not always intuitive to figure out the exact command.
cd /; tar cf - etc | ( cd /tmp; tar -xf - )"
replace the "cd /", "cd /tmp",and "etc" appropriately and you're all set. If you're copying system files you'll probably want to use "-p" on the extract side. Trust me.
Killing a range of processes
Recently, due to a wacky networking issue, I had some 200+ sendmail processes sitting around waiting for data that would never arrive. Since valid mail was once again flowing, I didn't want to bring down sendmail, or even -HUP every sendmail process on the system. Thanks to Linux's use of monotonic PIDs, though, I could see that all of the processes I wanted to bump off were in a certain range. The following ugly hack did the trick:
kill -HUP `ps ax |\
   perl -wne 'next unless /sendmail/ ; @fields=split() ; print "$fields[0]\n" if 9300 < $fields[0] && $fields[0] < 10565'`
Partition table backup
sfdisk -d /dev/sdX > backupfile
   sfdisk --force /dev/sdX < backupfile

Valid XHTML 1.0!