Other writeups here seem to cover the basic background information, so rather than repeat them:
Daria is one of my favourite programmes.
It just has that 'watchable' factor. I find it very funny even though there are no 'laugh out loud' moments.
It makes excellent use of MTV's archive of songs available. The inter-scene music may only play for 5 seconds but it helps the atmosphere of the show. Fun for all the 'name that tune' geeks.
Thanks to the dreadful treatment of the show by channels in the UK (and everywhere else if you listen to the fans abroad) I only got into it in 2000. But hey - I have that huge backlog of shows to see.
(By 'see' I mean 'download', you scum at MTV and Channel 5..)
You can find a load of episodes on the Gnutella network.
Here is a complete list of all episodes:
Season 1
Season 2
Season 3
Season 4
Season 5
Movies