jeffatrackaid - 7:12 pm on Jun 16, 2010 (gmt 0)
As lammert says, without a more detailed analysis of your system, making a recommendation about a new server is very difficult.
I use a program called sysstat to collect various disk, network, memory and cpu metrics. Based on this data, you can see if you have a hardware limitation or not.
In some cases, the issue may not be your hardware but system configuration problems, corrupted database tables, or a poorly optimized system. In this case, moving to new hardware may not yield the results you desire.
As it looks like you have a growing business, you may want to find a server management company to help you out. There are many 3rd party server management firms that can help you with performance issues, service sizing and the migration itself.