Serious Server Load

I have some serious server load issues on one of my web servers...

Hardware:
Intel Pentium D 3.40GHz
1024 MB DDR RAM

Software:
RH Linux with 2.6.9-42.0.3.ELsmp kernel
cPanel with most recent Apache and PHP 5.2.x

Process list (top output, on a regular moment):

[url]

When everything is running normal (read: server load below 2) there's between 100 and 300 MB of free memory. Though sometimes (this happens about 2 times per day, at random times of the day) the server load dramatically increases.

I wrote a script (the chkApache.sh process in the top list) that constantly checks the server load and if it raises about 4, it will check if the sum of all httpd processes are consuming too much CPU or Memory. In this case, it will force a httpd restart... I need this to prevent Apache from crashing my server almost daily. If I let Apache do its thing without this script, it will happen that tons of httpd processes (50 and up) take in all the RAM and server load increases to 100 or more and the eventually I need to reboot the server using the SoftLayer control panel.

That chkApache script I wrote also sends me a detailed report of the state of the server when it needs to restart Apache, here's a report of an event that occurred today (includes server load info, memory info, top list, httpd processes info, netstat, etc):

[url]

In this case you would think that someone is attacking the youthforums.co.uk domain but I doubt that's the case... It doesn't always happen with that site, in fact I can't seem to find a pattern in the Apache status page so I don't think a single account is causing this...

Today I also used the Apache JMeter to "stress test" my server. I was shocked when I saw how easy it is to use that tool in order to make my server crash... I used 10 threads loading one PHP page (that makes some MySQL queries) and made a loop that kept requesting that information, with 10 connections at a time... The server load rapidly increased to 30 and above... I think it's unacceptable that something like this can happen so easilly...

I tried several things with my Apache configuration settings... Here's what I have at the moment:

Code:
RLimitMEM 67108864
RLimitCPU 60
RLimitNPROC 30

Timeout 5
KeepAlive On
MaxKeepAliveRequests 50
KeepAliveTimeout 2
MinSpareServers 5
MaxSpareServers 10
StartServers 5
MaxClients 40
MaxRequestsPerChild 100

<IfModule mod_limitipconn.c>
<Location />
MaxConnPerIP 3
NoIPLimit image/*
</Location>
</IfModule>

LoadModule rewrite_module libexec/mod_rewrite.so
LoadModule expires_module libexec/mod_expires.so
LoadModule bwlimited_module libexec/mod_bwlimited.so
LoadModule bytes_log_module libexec/mod_log_bytes.so
LoadModule auth_passthrough_module libexec/mod_auth_passthrough.so
LoadModule php5_module libexec/libphp5.so
LoadModule security_module libexec/mod_security.so
LoadModule evasive_module libexec/mod_evasive.so
LoadModule limitipconn_module libexec/mod_limitipconn.so
Does anyone have an idea what's wrong here? Anything I can do to get more detailed information on what's causing this? I've been on this problem for weeks now but I can't seem to find any proper solution.

In case it matters I'm also running: SIM, RPM, BFD, APF and SPRI