Blogger

Blogger is a service that allows users to create free blogs. Its also provides space to host the blog, but users can also host the blogs on their own websites.

LiveJournal

LiveJournal is a blogging service that offers its users a social networking community in which to host that blog. The virtual community created by LiveJournal provides a degree of privacy not offered by most other blogs by allowing its users to restrict access to their blogs to users classified as 'friends.'

Wordpress

Workpress provides its users space to create a free blog. The service distinguises itself by offering its users many options for customization.

Librarything

LibraryThing is a social cataloging service were users can upload and share their personal book catalogs. Popular among librarians (go figure).

aNobii

aNobii is a social network aimed at booklovers.  Comparable to the music service Last.fm, aNobii allows users to share recommendations and reviews of their favorite books (or perhaps mutually  disliked books).  Users also have the option to rate books which aNobii takes into account when it makes its own recommendations. 

Last.fm

Last.fm is an online radio/online music community based in the UK, which boasts 15 million users based in 232 countries. Users can listen to portions of or complete tracks via Last.fm as well as interact with other users by comparing musical tastes and exchanging recommendations. Last.fm uses a plugin called 'AudioScrobbler' to transmit the titles of tracks played on the user’s computer or iPod which the service uses to create charts of top listened to tracks and to generate its own recommendations.

Pandora

Pandora is an Internet radio player that provides the user with recommendations based on tracks played previously on the Pandora site.

Word Processing

Spreadsheets

GoogleSpreadsheets
Zoho Sheet
Think Free
gOffice
NumSum
 

Presentations

Photo Editing

Photo sharing websites allow users to upload photos onto the website where they can then be shared with other users. After uploading photos to a photo sharing website, they can then be posted onto blogs, wikis or other Web 2.0 sites.

Flickr

Photobucket

Fotki

Flickr Mash-ups

Below are a number of third-party application which modify the functionality of the Flickr service.

Mappr - allows you to take Flickr images and paste them on a map

Flickr Color Pickr - lets you find public photos in Flickr that match a specific color. Montagr – create a photo mosaic from photos found on Flickr.

Online Readers

Bloglines

Bloglines is an online feed aggregator, which uses syndication technologies such as Really Simple Syndication (RSS) and ATOM in order to deliver blogs or news items to the users desktop automatically.
Google Reader

Google Reader is an online feed aggregator much like Bloglines.
 

Desktop Readers

Omia Reader (Windows)
Vienna (Mac)

Del.icio.us

Del.icio.us is a social bookmarking site that allows its users to tag websites with keywords. The body of tags (folksonomy) allow users to discover and share websites.

Digg

Digg is a website that takes advantage of social bookmarking in order to provide its users with news links. The Digg front page displays links to news items that Digg users have deemed to be relevant to the Digg community. This is decided by taking into account how many users have submitted the page to the Digg service. Digg also takes advantage of blogging and syndication technology.

Stumbleupon

Stumbleupon is an Internet browser plugin that allows users to rate and discover webpages. The unique aspect of this social bookmarking site is that it takes into account the users previous ratings when recommending the next site.

Reddit.com

Like Digg, Reddit is a social news website that posts news links which are displayed in order of their popularity as determined by Reddit users.

Diigo

Diigo is a social bookmarking service that offers the user the unique option to attach annotation to the tagged websites.

Newsvine

Newsvine is a social news site that allows users to have a dialogue about the tagged and bookmarked websites.

Bebo

Popular social networking site. In fact, according to Bebo, it is the most popular social networking site in Ireland!

Facebook

Social network that was originally restricted to college and university students and as a result is still very popular among that population though the site is now open to anyone. Numberous native and third-party Web 2.0 'apps' are available including photo sharing (including integration with such sites as Flickr), blogging, and syndication.

43 Things

Won the 2005 Webby Award for best social networking site.

LinkedIN

Social network aimed at establishing business contacts

MySpace

MySpace is by far the largest social networking website with approxiamately 192,000,000 users.  There are a number of services available to users through MySpace including blogs and instant messaging, ans it's getting bigger.  Since media mogul Rupert Murdoch bought the website, it has been expanding into many new areas.   

Orkut

Google's answer to social networking

Daily Motion

Daily Motion is a Paris-based video sharing website that allows users to upload and view videos. It also allows users to tag videos and offers a higher video resolution than the popular YouTube.

Metacafe

Metacafe is a video sharing website that offers its users a downloadable desktop client to view its high quality video clips.

YouTube

YouTube is a popular video sharing website that offers users a large selection of user-submitted videos.

PBwiki

PBwiki allows users to create their own wikis in about as much time as a blog entry (hint: you are using PBWiki right now).

Wetpaint

Another website that allows users to easily create wikis.