Firefox users have an easy first choice in the form of a free extension called ReloadEvery . It gives you everything you really need.
For Internet Explorer there’s a rather unimaginatively-named toolbar plug-in called "Auto Refresher for IE." Once installed, you have to enable it from View/Toolbars. It’s quite an old product but I found that it worked fine with IE7.
As with all auto-refresh utilities, make sure you turn these products off when filling in web forms, otherwise you may find you lose all your work.