SplitView
I installed the demo personal edition and could not get the boundaries to work properly. To be honest I felt 39$ was a little steep for what you would be getting.
Sizer
A good old tool from the 90's is a hidden gem unfortunately it is only 32-bit but this thing is an excellent and cheap alternative. Simply fire it up on your RDP host set your window sizes and positions and your off and running.
For Extra Credit-
If you hate browsing on your RDP host because it bogs down your RDP performance (flash ads mostly). Find a tool that allows you to set your client windows as "Always On Top" so you can use local applications over your spanned and maximized RDP session.
UPDATE: This solution is primarily geared to those of us still using Vista or XP as either a client or host. Those of you lucky enough to have both windows 7 at both ends can use the multimon feature: http://blogs.msdn.com/rds/archive/2009/07/01/using-multiple-monitors-in-remote-desktop-session.aspx