memory usage

[Jonathan Horne]

i have a server that has 2GB ram, recently upgraded from 1GB ram.  it runs 
apache2.0 with php5, sendmail with spamass-milter, dovecot, mysql5.0, cacti, 
and a couple other small things (like snmp, my bx irc shell, etc).

when ever i look at the memory usage (via phpsysinfo, or cacti graphs), its 
nearly always showing less than 100mb of ram available.  top shows several 
perls (probably spamassassin), 8 or so httpds (typical), but that would 
probably only account for (a liberal guess) 500-600 mb of ram.

is there a good way to find out where this bottomless ram funnel leads to?  
or, should this behavior just be considered typical?

thanks,
jonathan