I just found out that Telerik's creating a code conversion tool: http://converter.telerik.com/. It looks pretty slick with AJAX integration. No wonder because Telerik's been very busy on that part.
Another conversion tool that I used during the last couple of years are these: C# to VB.NET and VB.NET to C#.
Update: Gill pointed out in the comments that #Develop also has this functionality.