Why don't you try Solaris? There is no cost on using it, since no license fees are required (even for commercial applications).
If you are looking for support / maintenance packages as well, then you should find that it is very competitively priced against other commercial Linux systems (e.g. Redhat).
Of course there is no need to mention that Solaris is rock-stable it is a proven system.
There are other benefits too, such as excellent support for Java development tools (you can expect that much from Sun)