I host a handful of low traffic sites. I want to move to a VPS so I can continue with the small hosting biz, as well as have some custom software installed for my internal use.
I'm looking at buying the webmin plan from powervps. But I'm wondering if there is any option for a simple control panel for my users? I understand webmin might be useful for me, as the admin, but what can I offer my users, so they can change email settings, database options, etc...
I want to keep the total cost under $25 a month, so I guess cpanel and other commercial solutions are out of the question.
Just up your budget a bit ($10) and go with Steadfast. They offer Cpanel, Plesk, or DirectAdmin free. Webmin is not easy for clients to learn/use. Also, it will be much easier for you to setup Plesk or Cpanel than webmin.
A control panel will not run well on that Powervps plan.
Did you took the Bronze VPS with Cpanel ? 128 Mb of ram is not so much.
How is the server load ? Stable and low ?
At VPS, the lowest level Cpanel package (Cpanel1) has a guranteed RAM amount of 256 MB not 128 and burstable to 1 GB. Their servers have dual AMD opteron 248's with 8 GB of RAM. I was on this package for about six weeks before I upgraded to Cpanel 3 (for bandwidth and space) for about 6 weeks and saw no problems. In fact, even though I'm guranteed 768 MB on Cpanel 3, I don't notice a performance difference at all. But I definitely need the space and bandwidth.
To answer your original question, spend the extra few bucks a month and go with Cpanel. Yourself and your clients will thank you.