It was way back in 2001 when I was tasked at my company to implement our internal web application in ASP.Net. This site not only reported on most of the company's critical functions but also contained very complex data management screens. The sheer size of the site precluded it from being in a single dot net solution.
So, after many hours of searching the Internet in vain for a solution, I finally started to experiment on my own. I discovered that any project could be added to the site by copying the compiled DLLs into the sites bin directory. This works, but it is not the most elegant solution.
Well, many years to late, at least for the company site, I've discovered a much more elegant solution. (And when I say I've discovered it, I mean that I've finally found the information on the internet :-))
Here is the link to the original information:
This post refers to ASP.Net 1.1, but I've taken the time to verify that this still does work in ASP.Net 3.5.