Microsoft has posted a nice diagram of various extranet server farm topologies available for SharePoint 2010. The diagram includes advantages and disadvantages of each topology as well what the farm layout might look like. The included topologies are:
- Edge firewall
- Back-to-back perimeter
- Back-to-back perimeter with cross-farm services
- Back-to-back perimeter with content publishing
- Split back-to-back
- Split back-to-back optimized for content publishing
Download the document from:
http://www.microsoft.com/downloads/en/details.aspx?familyid=EB4BFF25-BABA-4112-B518-F2FC442D5467&displaylang=en