Notable Web 2.0 Sites

Recently read the August 2007 edition of Laptop Magazine which had a review of the 'Top 50 Web 2.0 Sites'. Some noteworthy ones (at least for me):

www.lifehacker.com (learn something new)
www.lifehack.org (compliments the first one)
www.wordpress.com (for blogs. open-source, cleaner than blogger)
www.centraldesktop.com (project collaboration for teams and there is always PBWiki)
www.dropsend.com (to send large files without having to set-up an elaborate FTP server like me)
www.mozy.com (for online backup/50GB - $4.95/mo. Then you don't have to keep purchasing external hard drives/tapes, etc)
www.citizendium.org (wiki w/ a conscience. Hard to tell how this one will fair. Too many people already use Wikipedia)
www.lala.com (cd trading. I have a ton of CDs that I could trade.. I'll have to look into this)
www.orb.com (to stream your stuff - videos/photos/music from your PC to ?)
www.joost.com (for TV stuff - not available outside the US)
www.jumpcut.com (edit videos w/out software)
www.kayak.com (travel site, yeah so what... there is travelocity, hotwire, etc... apparently this site searches all those sites)
www.airfarerwatchdog.com (for cheaper flights)
www.tripadvisor.com (for hotel reviews)
www.mapskrieg.com (goggle + craigslist real estate postings)
www.zillow.com (find out how much your house is worth or how much that house you're buying is worth)
traffic.poly9.com (google+yahoo traffic+weather)

I haven't checked all these sites out yet. Some look quite useful. I gave Citizendium a try by looking up 'Web 2.0' and it didn't have any results, so I still had to resort to Wikipedia.