Blogs:

http://www.aspirationtech.org/blog/nonprofitoperationsBlog on Nonprofit Operations Management by Aspiration Tech's Operations Director.  This blog provides information and education:

http://www.lahomelessblog.org/
Daily Blog by CEO of PATH, an homelessness charity in LA.  This blog provides editorial comment on homelessness and policy, as well as information on PATHs work and links to other information.

http://www.netsquared.org/blog/britt-bravo/teaching-young-people-with-blogs
Article and links on Teaching Young People using blogs:

RSS - really simple syndication:

Allows you to push news and other information out to people who want to subscribe to it:

http://www.ePath.org
example of an organization using RSS to push information out to increase visibility.

http://blueskycollaborative.typepad.com/blog/2006/09/rss_is_an_oppor.html
how to setup an RSS feed

Tagging & Social Bookmarking:

http://del.ico.us
social bookmarking site

http://toolcrib.ning.com/index.php/index/cloud?type=tags
uses tags as a way for people to categorize and search items in the online database

http://socialsourcecommons.org/tool/by_tag
as above.

http://www.flicr.com
allows pictures to be uploaded, tagged and shared

Online Collaboration Applications

create online docs & spreadsheets for yourself or to collaborate with others:
http://docs.google.com 
http://www.zoho.com

(Here's a document I have setup for anyone to see: http://docs.google.com/View?docid=d3vw6z4_2gwwmhn)

project management & collaboration:
http://www.basecamphq.com

setup a conference call for free:
http://www.freeconferencecall.com

setup an online meeting for free:
http://www.gotomeeting.com

instant messaging - see GAIM, MSN messenger, Yahoo etc etc.

Wiki's

Web pages that are open to editing and revision.

http://www.wikipedia.org
most famous example of a Wiki.

http://penguinday.blueoxen.net/cgi-bin/wiki.pl?PenguinDayAgendaSFBayArea2005
example of an event that used a wiki to allow participants to get session notes online quickly

http://docs.moodle.org/en/Teacher_documentation 
an example of a Wiki used to create documentation collaboratively.  (In this case for www.Moodle.org, free online class creation tool for Educators).

Mashups

two online applications combined to get a third!

http://flood.firetree.net/ combines Google maps with sea level data.

http://www.therenewableplanet.com/ combines Google maps with an editable database renewable energy projects around the world.

http://www.housingmaps.com/
combination of Craigs List and Google Maps.

http://moodle.org/sites/
moodle show how widely they are used across the world

http://www.programmableweb.com/matrix
a matrix trying to show all the current combination of websites and their data into something new (ie mashups!).

Social Networking

Organizations are looking at how they can use social networks such as www.MySpace.com, www.facebook.com and www.SecondLife.com to reach out or provide services to teenagers and young adults.

Early days, but take a look at this interesting use of YouTube by "Rock The Vote":
http://www.youtube.com/group/rockthevote

Nonprofit specific directories of online tools

keep an eye on these sites which are both under development.  As well as listings, they intend to add interviews, articles and examples that will help nonprofits put these tools in a practical context.

http://toolcrib.ning.com/ 
a participatory online directory created by the dotOrganize project.  Includes user ratings.

http://www.socialsourcecommons.org 
a directory of online tools, which uses social networking and tagging to help categorize and organize the information.  Created by Aspiration Tech.

Nonprofit Web 2.0 info & resources

http://www.techsoup.org/toolkits/web2/
links you to further articles and resources that cover this topic

http://www.aspirationtech.org
Aspiration connects nonprofit organizations with software solutions that help them better carry out their work.

http://www.netsquared.org 
provide a link to nonprofit applications of this technology as well as tools and innovators in this field.

http://www.dotorganize.net 
dotOrganize provides research, forums, and resources to assist organizers in utilizing online tools as vehicles for their vision.