Interesting Semantic Web systems

Watson: a gateway to the Semantic Web
DBpedia allows you to ask sophisticated queries against Wikipedia and to link other datasets on the Web to Wikipedia data

GroupMe!

A new kind of social tagging system that combines Semantic Web technologies and Web 2.0 technologies.

Interesting conferences (with some indicators of quality)

EKAW 2008 International Conference on Knowledge Engineering and Knowledge Management A [in CORE]
WI 2008 IEEE / WIC / ACM International Conference on Web Intelligence 0.86 [in CSCR]
WWW 2009 International World Wide Web Conference A+ [in CORE]
ECIS 2009 European Conference on Information Systems A [in CORE]
IJCAI 2009 International Joint Conference on Artificial Intelligence A+ [in CORE]
ESWC 2009 European Semantic Web Conference A [in CORE]
WISE 2009 International Conference on Web Information Systems Engineering A [in CORE]
K-CAP 2009 International Conference on Knowledge Capture A [in CORE]
ISWC 2009 International Semantic Web Conference (ISWC) A [in CORE]

Tutorials, reports, educational material...

Minding The Planet - The Meaning and Future of the Semantic Web (Nova Spivack)
A short Semantic Web tutorial (York Sure)
OWL tutorials
RDFa Basics

Other stuff about semantics and ontologies

The Ontology Alignment Evaluation Initiative
W3C Semantic Web Activity