Amongst all online collaboration solutions Basecamp is the best one I ever came across. 37signals is putting a lot of thoughts and efforts into the platform to keep it simple, purpose driven and extremely user-friendly. Unfortunately I am required to use a different platform at work which has yet to adapt the design principles of Basecamp.
Those that manage their personal tasks in OmniFocus and leverage Basecamp for collaboration are always looking to integrate the two. At least to a certain extent.
Ryan Irelan has updated and reposted his AppleScript based solution that uses Mail.app rules to accomplish this. Check out his original description for instructions and more details.
The beauty of Ryan’s approach lies in its simplicity and the fact that you can use it with tools you have out of the box and consequently free of charge.
For a more professional grade integration between Basecamp and OmniFocus you should give Spootnik a go. It uses the WebDAV sync capabilities of OmniFocus not only to keep your data the same across your devices, but also between Basecamp and OmniFocus.
Spootnik also fulfils two very popular feature requests for OmniFocus by providing an web interface to your data and allowing you to email actions directly to your inbox.
While you can test drive it for 30 days, the subscription model starts at 3$ per month.