If you have the time to spare, it’s definitely worth picking up a copy of Optaros’ Open Source Catalogue 2007 (it’s free). Most valuable is their perspective on current trends in the top-ranked projects: which are on the rise, steady, or on the decline. A few tasty tidbits:
The virtualization software XEN has positioned itself as a low cost and innovative alternative to commercial products such as VMWare. With every release stability and applicability are increasing.
The databases MySQL and PostgreSQL (respectively EnterpriseDB as the professional derivate of it) have almost caught up with the benchmark of Oracle in terms of functionality and performance. In many situations they might even fit much better than the industry leader.