I just got VPS with 128 MB of memory and it's too slow now, because of many httpd requests. I really need to optimize it extremely. When I say extreme optimization, I mean that all I need - fast working websites which use just php, mysql and some functions like cURL. I don't need any mail, syslog or similar services to be running. VPS is used for serving php pages only.
I tuned httpd.conf and my.cnf already. What other steps you recommend for me?
Yep, if you have tweaked your settings with the HTTPd and the php parser and still need it to go faster you would just have to get some better specs. If you want to tweak some more, and see exactly how its helping or hurting look at this: http://httpd.apache.org/test/flood/
I agree with others that you likely want bump up the memory to 256 MB. If that is not an option for you...I would turn off all services that you don't need. For example, if you are not using DNS or a mail server I would turn those services off.
Assuming that you are running your VPS on Linux try doing running the following to see what is running and what is not:
If there is something that is running but shouldn't I would disable that service.