Microsoft Press is handing out 3 books:
– Introducing Microsoft LINQ by Paolo Pialorsi and Marco Russo
– Introducing ASP.NET Ajax by Dino Esposito
– Introducing Microsoft Silverlight 1.0 by Laurence Moroney
Silverlinght 1.0 is probably a bit outdated (with 1.1/2.0 close), but the others should be good, judging by the authors. Dino Esposito wrote couple of very good books on ASP.NET and .NET.
See this blog for more details and download links.