Server Monitoring tools for single standalone server

[pita]

Hello,Pls suggest me some monitoring tools with low overhead, customizable & that can generate rrd/graphs (like mrtg ones)I need to monitor, general server stats like CPU, Loadavg, memory,vm/iostat, var/log/messages, port 80/apache, monitor few services/process, networking stats,uptime. And few other things I can a write a perl/shell scripts to do it.I dont have much experience outside enterprise type softwares which I think are ill suited for a single server monitoring standpoint. Oh yea os is Linux.