On Unix, I generally use ( sleep 60m; xterm -bg red ) & to set a timer to pop up a big red window after an hour, without tying up the shell.
Some of my favorites:
Scan a log file generated by strace -tt, looking for each second turnover: (should statistically find the operations requiring the most time)
Print out a running sum of the 3rd column of a file:perl -lane 'print $last if ($F ne $lastt); $last = $_; $lastt = $F[ +0];'
Rewrite all of the CVS/Root files in a tree (yes, this is a weird way to do it):perl -lane 'print $s += $F'
Print out all the double-quoted strings in a file:find . -name 'Root' -print0 | xargs -0 perl -i -pe '$_=q(:pserver:sfin +k@cvs/usr/local/cvs)'
Somewhat more robust version (handles backslashes):perl -lne 'print $1 while (/\"(.*?)\"/g)' filename
Print out all of the C++ constructors in a set of files:perl -lne 'print $1 while (/\"((\\.|[^\"])*)\"/g)' filename
I don't know if those are really representative of my favorites. I normally just spew them out on demand, so it's difficult to think of them when I don't actually need them. The above are just the ones I've used recently enough to remember.perl -lne 'print if /(\w+)::\1/ .. /^\}/' *.cpp