Bluecoat, Citrix, F5, Riverbed and other similar vendors all offer highly functional and well performing WAN Optimization appliances. Unfortunately, those high-end solutions can be either overkill or over budget for some organizations. So, instead of buying the whole pizza, why not try a slice first?
I don't think there's an IT Manager out there who is happy with the bandwidth they have on their WAN links. WAN bandwidth feels like a paycheck sometimes: you're never quite happy with it and you always want more. The reality is that we all need to work within our budgets and get the most out of what we have, and if you don't have the budget for WAN optimizations now, then you need to get creative.
Surprisingly, you can actually introduce a somewhat effective sliver of WAN optimization via Windows Server 2008 BranchCache. BranchCache doesn't do TCP compression or acceleration in the traditional sense, but it does lighten the load on the WAN through its ability to serve out frequently accessed content at the branch office.
Organizations that enjoy active Select, Enterprise or Open licensing agreements can essentially add BranchCache for no money up front. Sure, you'll need to true up with Microsoft at some point and pay for the extra server licenses, but if you have the hardware sitting around, you can at least implement a short term solution for lightening the load on your WAN links.
Aside from BranchCache, Microsoft tweaked the TCP stack for better performance in Windows 7 and Windows Server 2008, and it optimized SMB for better CIFS performance. We're not saying to scrap your plans to buy Riverbed, but if dollars are tight, and you're already deploying Server 2008 anyway, assess what Microsoft is giving you out of the box. It might be "good enough" for your needs.