Lots of times, albums are uploaded with no scans at all or maybe just really tiny ones. Where do you go usually to get your covers? What sites have the best scans, widest selection, or most complete album art?
For me, my first stop would be www.allcdcovers.com. They have a pretty huge selection of CDs as well as DVDs now. While some of the scans are not really high quality, the sizes generally range around 1200 to 1400 pixels. And they include a lot of the album art like back cover, inlays, and CD itself. Most scans will be downloaded as jpgs.
The downside here is that after about 8 or 10 downloads, you get hit with an anti-robot "please enter the below code to continue" prompt and you end up downloading a huge bmp file instead of a nice jpg. After this download, you're back to pulling down jpgs again for a while. So it's really just a bump in the road if you're going after all the art for somebody's discography, for example. Still worth the trip.
dr.g

I've never looked at "Google Images" .. don't even know how to get to that spot. I usually go to Amazon.com music section and copy theirs. Or occasionally to the artist's website, or even to a "Coverart" website sometimes.

http://www.coveralia.com/

wikipedia gives album art pic

amazon!

Google Images

Google, with a spot on search say like "The Cramps Bad Music For Bad People Cover" you will get good results, then just save the image and upload to img host site grab the img code and attach to the description of the torrent. Now agreeing with vague amazon can be good for this, on albums it knows, horrorpunk on the other hand is a bit underground so not every site has a full detailed index on every band and cover so some are really hard to find.

Google images usually comes up with the goods

When I can't find an album cover photo at the usual places (Amazon.com, Wikipedia, the artist's website), I've also used www.discogs.com. Discogs also has a LOT of information about the music not available elsewhere!
It's important (to ME) to have the composer's name(s) in the tagfile - and the names of other singers on a music tract. I've become more obsessive about my collection over time. I've found that some songwriters are also performing artists... and the best song writers have written the songs/lyrics for many of the best songs available. I've found some great new music simply by reading up on the music I have. Discogs is a great resource for info on composers, song writers, AND the albums/songs themselves.

I make all of my album art completely myself using 3dsmax and Photoshop, and sometimes photography I've taken from a camera.