This is sort of my ideal 23, not necessarily for librarians, but the things I find important.
1. One massive multi-online role playing game (MMORPG) that is NOT Second Life. Repeat, NOT Second Life! I don't know why librarians think this is so great but its not. I've only ever met two people IRL that played second life and one of them was my sister who is always looking for ways to make money and she had heard that SL might be a good way. The other was the TechNet 2008 main speaker who hilariously told the audience that they might even want to be furries on second life if they like cats. I am afraid she doesn't know what kind of negative, sexual connotation being a "furry" is.
2. Facebook--for obvious reasons.
3. Myspace--because FB and Myspace are two separate identities with very different missions and people on them. Some overlap, but not all. Our lower income people use this.
4. A useful online photo manipulation website such as http://picnik.com. This would be much more useful to librarians in general than how to make a lolcats poster. And it would also free up money from having to buy Photoshop for people who only use it to crop and touch up pictures.
5. Flickr does go along with the previous post but I think any site like Flickr should mainly be in context of how the library can use the content (creative commons).
6. RSS Feeds--we use these at our library and it would be good to let the staff know what they are
7. blog readers--useful tool for librarians to keep track of professional development blogs... although I've personally noticed specifically library blogs are not that up to date or relevant anymore.
8. Tagging in a library context
9. delicious-- we are going to try to use this instead of old style link lists on our website.
10. Library Thing--in context with tagging, like the Bedford Public Library's site.
11. blogs--our staff isn't even all that familiary with blogs in general much less blog readers
12. widgets--widgets are tools that make other sites part of your site and vice versa and that is a useful marketing tool/relevancy issue
13. instant messaging--focusing on ask a librarian type things. We use meebo in a limited context right now.
14. twitter/texting--since twitter is so similar to texting, I think these should be lumped together.
15. Online Video--I think YouTube is too simplistic. I think this should encompass more than just youtube. Youtube is a brand... "vodcasts" existed before these... and will continue to exist afterwards.
17. "Learning 2.0"--except I think 2.0 isn't anything except a faster form of distribution... I challenge people to learn... especially from presentations such as this:
I don't know what else would be useful... but not wikis or podcasts...