Even if you decide not to build your own Building Block or PowerLink, there are still ways to find tools that meet your organization's needs.
The Building Blocks Catalog is a comprehensive searchable listing of commercial and free/open source Building Blocks. It can be accessed here.
The PowerLinks Showcase is a listing of many commercial and free/open source PowerLinks. It can be accessed here.
Clients who have wanted to share their finished Building Blocks and PowerLinks have a space to do so here.
Blackboard has also contributed several free or open source Building Blocks and PowerLinks to the community. Click here for more information.
OSCELOT is an open source developer community that focuses on developing educational tools. Their site hosts releases of free/open source Building Blocks and PowerLinks.