After long thoughts decided 70-340: Implementing Security for Applications with Microsoft Visual C# .NET should be the next exam.
70-229 and 70-230 should be out soon with a new exam for new products Yukon and BizTalk 2004.
Before .net, i was one of the strong believer Security and Microsoft doesn't go well together. With the amount of intrest/efforts MS is putting for the security, this exam deserves a credit.
Started reading the following books, i hope it helps.
Whatever should get MCSD.net certified, before the certified counts jumps to 5 digits.
http://www.microsoft.com/learning/mcp/certified.asp (As of now nudjing close to the 10K)