The subject of using SharePoint as an Extranet has come up in conversation a few times recently and I was wondering if the community pursue this option in their Farms? We used a very cool Extranet tool called Extradium on SP24, but I know there are other options out there (such as doing your own Forms Based auth). I am really interested to see how you do it? If you do extend SharePoint to your partners do you go for a completely separate Farm running SP Foundation? We also offer a solution to help manage third-party risk so would love to hear your thoughts on that.
External users can access to SharePoint through ISA server as Jason said. We have developed an app (m1-Share) which enables users to access SharePoint outside the organization. You can check the app details at m1-share.com. Do let me know your feedback.