I was writing a class to hadle the caching of objects for the ASP.NET application I'm currently developing, and suddenly wondered if I could access the current HttpContext from within a static method. The answer, of course, is yes..
System.Web.HttpContext context = System.Web.HttpContext.Current
Another quick and easy answer thanks to .NET 247.
UPDATE: Thanks to Scott (see comments below) for pointing out you can also access the Cache directly via the HttpRuntime class, without requiring a context.