PRG pattern, out-of-the-box support
Built-in support for the PRG (Post, Redirect, Get) pattern. Possibly, through controller action filters ?!, along the the following line: http://weblogs.asp.net/rashid/archive/2009/04/01/asp-net-mvc-best-practices-part-1.aspx#prg
Bad idea. At my company, we outright ban TempData and all sessions due to the way our load balancing works in high availability scenarios. TempData is a kludge!