As Jacques said, it is almost always a bad idea to use regexes to try to parse HTML (or XML, for that matter).
If you really want to go this way (which could possibly possibly be tolerated for extremely simple operations), you could try something like this:
which means an opening <, followed by a number of anything but a closing >, followed by a closing >.
This is simplistic, but at least it will not consider this:
<center><b><font face="Verdana">Foo Bar </font></b></center>
as one single long tag starting with the opening < at the beginning of the line and the closing > at the end of the line above, but will be more or less able to match tags individually.
However, this will break, for example, if the tag spans over more than one line or in many other circumstances. In brief, don't do that except possibly as a one-shot script for extremely simple substitutions.