Funnily enough, after having just stated this on MacInTouch, Apple, today, added a user enabled download artwork link to their official "Link Maker" web site:As for artwork, I prefer hi-quality artwork, as it looks amazing when playing back via an Apple TV on a 1080p HD television. This requires sourcing at least 1000x1000-pixel artwork, which is not easy. Fortunately, I have found a way to grab hi-res artwork from Apple's iTunes online library, which I can't post here, as I don't want Apple to shut that route down.
Select Media Type > Music and then enter your search terms. Click on the song/album artwork you want and the "Download Artwork" link is at the bottom :-)
Full disclosure: the "11l7jb" part of the link above is my iTunes affiliate ID - it doesn't affect your ability to use the Link Maker/download artwork, and it is always appreciated if you use before purchasing on iTunes, as it all helps fund MacStrategy.