Websites of design associations, image databases, indexes and product information:

General

Artsource
Digital Resources - Society of Architectural Historians
Material District
- A free accessible search engine for materials.
Voice of the Shuttle: Architecture Page
WikiArquitectura
- Online architectural encyclopedia with most relevant architects & buildings from all time periods.

Canada

Biographical Dictionary of Architects in Canada 1800-1950
Canadian Centre for Architecture
Canadian Society of Landscape Architects
Centre for Landscape Research (University of Toronto)
Canada Mortgage and Housing Corporation (CMHC)
CWAHI (Canadian Women Artists History Initiative)
Design Exchange
National Research Council Canada
Ontario Association of Architects
Ontario Association of Landscape Architects
Royal Architectural Institute of Canada
Society for the Study of Architecture in Canada
TOBuilt: a database of buildings in Toronto
Toronto Society of Architects 

Image Databases

AGRAM Database: Architectural Information
Cities and Buildings Database
Great Buildings Collection
 

Indexes

API: Architectural Publications Index
- Accessible through the online catalogue of the RIBA British Architectural Library. On the RIBA Library Online Catalogue search page, select 'Advanced Search', scroll down to 'collections' and choose 'articles'.
Archindont: Architectural Index for Ontario (Toronto Reference Library)

Varia

American Institute of Architects
American Society of Landscape Architects
archINFORM - International Architecture Database
The Architectural League of New York
ArchNet
-Focused on architecture, urbanism, environmental and landscape design, visual culture, and conservation issues related to the Muslim world.
The Bauhaus Archive / Museum of Design
Chicago Architecture Foundation
Designinform Research Guides
furniture link
Library of American Landscape History
Pritzker Architecture Prize
Project for Public Spaces
Royal Institute of British Architects
Sustainable Design Resources (UC Berkeley)
Urban Land Institute

Blogs

ArchDaily
- The most visited architecture website in the world with news, interviews and commentary.
A Daily Dose of Architecture
BLDG BLOG
Lee Bey
- The blog of former architecture critic for the Chicago Sun-Times, as well as an architect at Skidmore Owings & Merrill.
Stuck in Studio
- A website created just for architecture students -- offers a community space for discussion, blog, and a resource page with job postings, competitions and tools.