Yahoo!
For me it is the most useful site on the net. It really is the one stop site ( I use its email, briefcase, photos, groups, calendar, add book, notepad, games, geocities, my yahoo!, greetings, astrology (most accurate in my case )messenger, and the toolbar, phew! ) I know all of you know about that site, but still that site is so convinient so had to mention it :)

Then there is Livejournal
(a blogging site)


Village Photos
Its the only site I have come across that allows hotlinking of images (i.e. you can store your images (a limit of 25 for free users) here and then link to them from any site)


Online Rail Ticket Booking
Indian Railways site allows one to reserve tickets via net.


Will add to this list later, meanwhile you guys also post the useful sites here, even if you think others might know about those sites, who knows may be someone does not know about them :)