Comics Continuum. The site doesn't seem to have a search function, so I looked on Wayback Machine. Not only does the Wayback Machine have the old pages archived, images and all, it turns out the pages are still live too! Choose a date, and then when you're on the archived site, look for solicitations at the bottom of the page - there'll be links to at least Marvel's and DC's. You can then remove the web.archive.org part of the address (just leaving in the bit from the http:// onwards) and you'll get to the still active version of the page on the real site. Also, if you know what date the solicits were released on you can actually figure out the URL. The archive goes back as far as 2000, as
this page proves (includes Marvel solicits for September 2000).
https://web.archive.org/web/20110715...continuum.com/
For example, here's the solicits for May 2011.
http://www.comicscontinuum.com/stori...2/14/dcmay.htm