SQLTypes compared to SQL Server Types
Tomorrow I will be speaking on writing SQL CLR Stored Procedures. Among other things, one thing you always want to insure is that you limit type coersion as much as possible. This means that you should use the SQLType library in your .NET code and the appropriate SQL Server types in the T-SQL Function that calls the .NET method. To insure that you use the right types here is the MSDN reference page of the data types mapped to each other.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemDataSqlTypes.asp
For other tips come listen to the webcast (or play the recorded version if you're busy tomorrow morning)