Monitoring changes over time...

If you need to run a command repeatedly at some interval and watch the output and know what has changed from the last iteration. For example say you want to monitor an XML feed which is providing data from weather sensors and you want to see the data every 2 minutes and also see the new data highlighted? try the Unix watch utility. It has parameters to specify update interval and also supports matching wildcard.

Monitoring multiple log files simultaneously

Ever wanted to look at many log files in real time while it's being updated? Multitail is a Unix utility program which can be used to monitor multiple log files and it will break up the display console into one unit for each file. It can also use colors while displaying the logfiles (through regular expressions). Supports monitoring wild card and more. You can monitor entire directories of files.
Also runs on Cygwin.