We use our hospital's website also.
I use the site, volunteermatch.org - it works great and it is free. I get some volunteer requests from there and have accepted some in too.
WE just use our hospital website no other program. In the past we did use voluneermatch but didn't work for us.
Could anyone share the sites you use to advertise volunteer openings that get good results. Please specify if the site is free. If there is a fee how much. Any help would be greatly appreciated.