If your MySQL server keeps crashing, it's time to file a bug report. Even though MySQL is thoroughly tested, there might still be rare bugs, and you should know how to begin to diagnose this kind of problem.
First, you should make sure that it is actually the MySQL server that is crashing and not your client program. Check the amount of time that the server has been up by issuing the mysqladmin version command. The output contains a line like this:
Uptime: 109 days 23 hours 31 min 51 sec
In this case, the server has been running for a long time, so it is clear that mysqld did not crash. Instead, you need to debug your client program.
If the uptime reported is very small or mysqld is not running at all after a suspected crash, the first step is to check that your tables are not corrupt. Stop mysqld and run the following command from the data directory to check every table in the system:
myisamchk --silent --force */*.MYI
Restart mysqld with the --log switch, or add log to the [mysqld] section of my.cnf. Every SQL command is logged to a file, and you should try to find a way to reproduce the crash consistently using the same command. You should then query the bugs database at http://bugs.mysql.com/ before filing a bug report.
Another possible cause of your crashes is an underlying hardware problem. In particular, faults with your system's RAM or hard drives can cause peculiar errors in MySQL. Perform a thorough check on your system's hardware if you experience intermittent, unexplained server crashes.