A while back, I came across 20 Tips to Improve ASP.net Application Performance.
It's a great list of tips and tricks you can take advantage of increase ASP.net performance.
One little gem I discovered in the list is the App_Offline.htm file.
It's a cool feature of ASP.NET 2.0 that allows you to quickly and easily take a site down for maintenance while sending users a friendly message. Just drop a file called app_offline.htm in the root of your site.
NOTE: There is one caveat that you should be aware of if you App_Offline.htm is less than 512 bytes, and Internet Explorer's "Show Friendly Http Errors" is enabled those users will see the generic status code message. See Scott Guthrie's post here to learn more about this, and a quick and easy workaround here.