Society of Systematic Biologists

Here are a few links to resources in systematics and biodiversity informatics. The list is deliberately short as Google searches are more likely to be effective than a long list of links, many of which will break sooner or later.

Databases and search engines
TreeBASE - published phylogenies.
uBio - Universal Biological Indexer and Organiser.
GBIF - Global Biodiversity Information Facility.
BOLD - Barcode of Life Data Systems.
BOLD - species search engine.
NCBI - National Center for Biotechnological Information, home of PubMed and GenBank.

Software
Joe Felsenstein's list - the mother of all software lists.