Barely five years old, Flickr has transformed the way we think of digital photography. Tagging makes exploring images easier, group pools enable users to collaborate on anything from art to breaking news, and unlimited uploads means Flickr Pro accounts are among the few things online worth paying for. Yahoo bought up the site in 2005.
Wikipedia is an extraordinary achievement, a compendium of knowledge that cost nothing to create and costs nothing to access. Are there errors? Of course there are - just as there are in printed encyclopaedias. Try fixing errors in those overnight. Wikipedia is awesome, and it's one of the single best things about the Internet.
While many virtual banks appeared and disappeared over the decade, PayPal has gone from strength to strength. It's not the prettiest or cheapest way to wire money around the world, but it's safe, solid, secure and enormously successful. eBay bought it in a $1.5 billion deal in 2002.
What did we do before YouTube brought us videos of cats falling off skateboards? YouTube isn't here for that, though: it's a media channel for dissidents in Iran, it's the home of viral marketing, and it's rapidly becoming a broadcaster in its own right. It's also offering increasingly high quality: in recent months we've seen more and more YouTube content in HD, and now it's moving to 1080p HD. Its brightest idea, though, was the Embed button, which enables site owners and bloggers to add YouTube clips to their sites in seconds.
Could Spotify be the Holy Grail of digital music? It's certainly generated acres of press coverage, but more importantly it seems to be making a dent in file sharing - something the music industry has tried and failed to do for a decade. Spotify is digital music done right, offering decent sound quality, a decent collection of music and, if you go for the premium version, a superb mobile phone client that enables you to take your music with you.
Not so much because of search - although of course Google ends the decade as the King of Search - but because of Google's other adventures, from Google Docs and Google Maps to Chrome and the forthcoming Chrome OS. What Microsoft was to the 1990s, Google is to the noughties.