You have a lot of options for this. Since your switching out equipment completely this wouldn’t be a bad choice to go gigabit since that will soon replace 100mbps.
If you know how to use Cisco equipment, a Cisco 4500 would be my choice. Otherwise, Juniper has a new line of switches which seem to be easily manageable. I suggest you do some research and figure out which equipment vendor you would personally feel confortable in managing.
Take a look at this tutorial on network switching.