If you already have a heavy investment in Documentum and need a better User Interface and accessibility to the data, take a look at using SharePoint as the front end.  It no only allows for direct access to data but also discoverability and an avenue of creating composite applications.  These tools allow you to leverage SharePoint for your enterprise portal and leverage Documentum investment for record management.

1. Wingspan DOCWAY  http://www.wingspan.com/default.asp?id=serv_sharepoint

2. EMC Content Services for SharePoint  http://www.emc.com/products/detail/software/content-services-sharepoint.htm

3. Vorsite Enterprise Productivity Suite for SharePoint http://www.vorsite.com/SharePointSuite.aspx

4. Microsoft Enterprise Search Indexing Connectors (formally known as Protocol Handlers) for EMC Documentum 5.3 (Service Pack 4) http://blogs.msdn.com/enterprisesearch/archive/2008/05/27/announcing-release-to-web-of-documentum-and-filenet-indexing-connectors.aspx

P.S.  If you are looking at making an investment into Documentum, please contact your Microsoft Account team to discuss your options.