The ones I "use" are:

Eng-tips.com (of course)

efunda.com

engineering.com

Sure there are pleny others out there, so will keep an eye on this post for others.

Personally, I would add the links to (all of) the preferred vendors of your company.  Also include the everyday links to find general parts such as
www.mcmaster.com and
www.grainger.com.

My favorite one, in case you need military specifications, is http://assist.daps.mil, where you can download, for free, several military specifications.

I assume you're using a CAD system.  A link to their homepage may be beneficial.  Often times they have little tips and tricks which may be of benefit to your engineers to glance at occasionally.

Don't forget about other popular organizations: www.asme.org, web.ansi.org, www.sae.org, www.osha.gov, www.uspto.gov, www.nspe.org, www.thomasregister.com.

My favorite material and fastener sites: www.matweb.com & www.boltscience.com

I should just send you my favorites folder.

--Scott

Hi Motorhead:

Here are a few more suggestions:

http://www.techstreet.com - standards, books etc.
http://www.geonetservices.com - online applications
http://www.waveone.com - online applications
http://www.redvector.com - online courses
http://www.verticalnet.com - engineering
http://www.myplant.com - engineering
http://www.engineering-e.com - CAD/CAE

Gordan

Visit the Engineering Software web site -- http://members.aol.com/engware -- where you can find free on-line calculators, demos and other material/information related to energy conversion systems (power and propulsion) ...

add these to your list:
www.machinist.net
www.ex.ac.uk/cimt/res2/calcs/caltri.htm

Add the following:

www.icrank.com ;    (Mechanical Engineering)
www.memagazine.org (Mechanical Engineering Magazine)
www.imeche.org.uk ; (Institution of Mechanical Engineers)
www.lindahall.org ; (Engineering Societies Library)
www.mhia.org ;      (Material Handling Industry of America)

For structural analysis of machine components, I like http://euler9.tripod.com/.
For military specifications, I like http://stinet.dtic.mil/str/dodiss4_fields.html.
For forum, I like http://groups.google.com/groups?group=sci.engr.mech.
For looking up detailed technical answers, I like http://groups.google.com/advanced_group_search.
For web page searches, I like http://www.google.com/advanced_search or http://www.altavista.com/sites/search/adv.

Try my web site www.gowelding.com it contains information on:-

Welding standards
Welded joint design calculations
Fatigue of welded joints
Basic Fracture mechanics
And more
+ links to many other sites