Here are some sites that we find to be particularly useful: 

AATA Online
https://aata.getty.edu/
AATA Online is a free research database containing abstracts of literature related to the preservation and conservation of material cultural heritage. It has been managed and published by the Getty since 1983. 

American Institute for Conservation of Historic and Artistic Works (AIC)
http://www.conservation-us.org
AIC's website features extensive conservation resources including guides, brochures, manuals and on-line courses regarding the conservation of architecture, books, ceramics, glass, furniture, objects, paintings, photographs, works on paper, video and textiles.

Ball State University Online Resources for Historic Preservation
http://www.bsu.edu/library/collections/archlibrary/onlinehpres/
Ball State's Architecture library maintains an on-line image databases, e-journals, preservation resources and links to other online sources and organizations.

Connecting to Collections: A Call to Action
http://www.imls.gov/collections/index.htm
Created by the Institute of Museum and Library Services (IMLS), Connecting to Collections is a national initiative to raise awareness and inspire action to make collections care a top priority.

Connecting to New York's Collections Resources
www.c2cnys.org/resources.html
A comprehensive listing of resources relating to the collection types covered in New York's Connecting to Collections Implementation Project, administered by Greater Hudson Heritage Network

Conservation On-Line: Resources for Conservation Professionals (CoOL)
http://palimpsest.stanford.edu/bytopic/genpub/
CoOL offers extensive resources and information on various aspects of museum preservation and conservation.

dPlan: The Online Disaster Planning Tool
http://www.dplan.org/
dPlan Arts Ready is an online tool developed by the Northeast Document Conservation Center and the Massachusetts Boards of Library Commissions. It is a paid subscription service that allows users to create a comprehensive disaster plan for their institution.

Heritage Preservation Service's Historic Landscape Initiative
http://www.nps.gov/history/hps/hli
This National Park Service website has a number of resources for those dealing with cultural landscapes, including case-studies, guidelines for the treatment of landscapes, preservation briefs, and publications.

Historic Buildings
http://historicbldgs.com/
Historicbldgs.com offers resources for historic building owners to help them preserve, repair and maintain their structures.

The Library of Congress Built in America
http://memory.loc.gov/ammem/collections/habs_haer
Built in America offers on-line access to the Historic American Buildings Survey (HABS) and the Historic American Engineering Record (HAER) collection of the Library of Congress.

Minnesota Historical Society
http://www.mnhs.org/preserve/conservation/
Minnesota Historical Society features on-line collections care resources and emergency response information, as well as specific resources on the preservation of American Indian objects.

Museum-Ed
http://www.museum-ed.org/index.php?option=com_content&view=section&layout=blog&id=5&Itemid=37
Museum-Ed strives to meet the needs of museum educators by providing tools and resources by and for the museum education community.

MuseumPests
museumpests.net/
A comprehensive guide with information and support for those implementing integrated pest management policies and procedures in collections-holding and cultural heritage institutions.

National Agricultural Library Rural Information Center (USDA)
http://www.nal.usda.gov/ric/ricpubs/preserve.html
The USDA provides web links to full text "how to" information, guides and manuals regarding various aspects of historic house preservation.

National Center for Preservation Technology and Training (NCPTTP)
http://www.ncptt.nps.gov/
NCPTTP has preservation resources from the National Parks Service Cultural Resources department available on their website.

National Trust for Historic Preservation and Conservation Resources
http://preservationnation.org/issues/sustainability
This section of the National Trust website is a great reference on the convergence of historic house preservation and green facilities management.  It includes case-studies of rehabilitation projects that include "green" aspects, speeches on sustainability, facts and figures, blog entries, news items, information on the Trust's Preservation Green Lab, and excerpts from the November 2008 Pocantico Proclamation for Sustainability and Historic Preservation.

New York State Historic Preservation Office (NYSHPO)
http://www.nysparks.state.ny.us/shpo/
NYSHPO's website provides online resources and technical assistance for historic properties.

New York State Historic Preservation Plan, 2009-2013
http://nysparks.state.ny.us/shpo/planning/index.htm
The latest state historic preservation plan put out by The Preservation Field Services Bureau of New York State.

Northeast Document Conservation Center (NEDCC)
http://www.nedcc.org/home.php
NEDCC is a non-profit conservation center that specializes in the preservation of paper-based materials. The website includes preservation leaflets and guides, resources for private collections, a list of suppliers, toolkits and print and web publications.

Northern States Conservation Center
www.collectioncare.org/
The Northern States Conservation Center features on-line resources regarding collection care, preservation and conservation treatment.

Old House Journal Online
www.oldhousejournal.com
Old House Journal Online features the National Park Service's "how-to" resources regarding historic preservation, maintenance, and restoration.

PreservationDirectory.com 
www.preservationdirectory.com
Preservationdirectory.com provides on-line resources on historic preservation, building restoration and cultural resource management in the United States and Canada.

Preservation101.org
http://unfacilitated.preservation101.org/loggedin.asp
Presented by the NEDCC, preservation101.org is an online course that focuses on the preservation of paper and related formats. Topics include the deterioration of paper collections and film and electronic media, the building and environment, treatment options, disaster planning and the building of a successful preservation program.

The Secretary of the Interior's Standards for the Treatment of Historic Properties
http://www.nps.gov/history/hps/tps/standguide/index.htm
Standards of preservation practices to help protect cultural resources.

STASH
stashc.com/
Provides information and tools so that institutions of all types, sizes and resource levels can learn how to create safe and appropriate storage solutions, written by collection care professionals.