Some links are out of date - I apologise for that!

• The www-server for ecological modelling is a great resource. It has:
  • Links to ecological models
  • Links to software, tools and databases
  • Links to literature, websites on modlling methods and research groups
• FOOTPRINT
  • Has data about virtually all active ingredients of pesticides
  • Lots of information, parameters on fate & effects
  • Quality controlled, quite reliable and consistent
• US EPA Ecotox database
  • Lots of ecotox data
  • Unfortunately has lots of inconsistencies and can't be used without checks
• The Umweltbundesamt of Germany (UBA, "EPA of Germany") has a very nice collection of links to databases with information about:
  • Chemical properties and toxicological data
  • Substance use
  • Environmental quality standards
    
• The Global Portal to Information on Chemical Substances
  
  • Integrates over 20 different databases and sources (and keeps expanding)
    
  • Chemical substance search
    
  • Chemical property data search
    
  • Physico-chemical properties, fate, toxicity, ecotoxicity, ...
    
• SRC free tools
  • Has free physico-chemical properties database
  • QSARs
• Interspecies estimation correlation
  • Interesting idea, based on a lot of data
  • How much trust can you put into these predictions? I'm not sure, but better than no information...
• The IRAC mode of action classification
  • Has nice MoA posters
  • Good explanations, reliable 
• Agency for toxic substances registry
  • Lots of useful information and links
• Online SMILES calculator
  • Both ways, you can also draw a molecule and get the SMILES notation
• Online Kow calculator
  • Uses many different QSARs
• Chemicalize.org
• • Great for chemical properties and molecular structures
• Sangster's Log Kow database
  • List of measured values
  • With one recommended value
• The freshwaterecology database contains information on
  
  • autecology and
    
  • geographical distribution
  • of european freshwater species
• The opentox website has
  
  • software for predictive toxicology and
  • is a developer and user forum
• The Knowledge Network for Biocomplexity (KNB):
  
  • has lots of datasets related to biodiversity and ecosystem functioning
  • and links to software
• The Environmental Health & Toxicology database:
  • has links to lots of databases with chemical and toxicological data
  • as well as many links and ressources for the general public
  • also has medical related information
    
• The University of Minnesota's biodegradation pathway database:
  • Biodegradation of xenobiotics
  • Biocatalytic reactions and pathways
• The toolbox of the CEFIC LRI initiative has many usefool tools:
  • Human health models and databases
  • Environmental models
  • Biotransformation and PBTK models
    
• There are several data repositories for scientific data:
  • A list of repositories is maintained by the Open Access Directory
  • Another list of repositories is maintained by the University of Oregon
  • Dryad is one repository with relevant data, but it's too early to know which repositories will be around in the long term...
• Another database hosted by the US EPA with ecotoxicty data (mostly pesticides)
• Here are some links to Environment & (human) Health databases and websites:
  • Agency for toxic substances & disease registry
  • European Commission website on Environment & Health
  • IRIS, US EPA's Integrated Risk Information System
  • International Programme on Chemical Safety
  • TOXNET, Toxicology Data Network bu the US National Library of Medicine