Doug: Happy weekend, everyone! Today I thought I'd just post a list of some of the resources I use for the work Karen and I do around here. In the comments section, feel free to add "good stuff" that you use or would recommend. What I won't list here are the many fantastic blogs that are out there -- these will mainly be database-type sites for comics knowledge and/or images.
This is a nice site -- by no means comprehensive. But the images are generally good.
I use the Comic Book Database most often when posting covers and for creator information. It's also handy to use when wondering if and where certain stories are reprinted. The creator biographies are nice, and I really love the chronological listing of character appearances or creator works. I've also used the site for the covers/corner boxes posts when looking for what was published in a given month/year.
Cover Browser is a great site -- this is one I use most often just recreationally, as they display up to 50 covers on a page. This site is pretty comprehensive, although I suppose they are lacking a series here and there. There isn't a lot of additional information -- even cover art credits are pretty rare. Another small drawback is that some of their scans are of CGC-graded books -- that really clouds the cover image and is a distraction. But overall, I'd highly recommend a tour of this site!
I'll admit to not having used the DC Comics Database, nor the Marvel Comics Database very much, but from what I have seen, both look useful.
Maybe the granddaddy of them all, the Grand Comics Database. While I prefer the format of the Comic Book Database, I do use the GCD for cross-referencing. There have been times when I've questioned a creator credit on the CBDB and felt better about the information I found on the GCD. It's for the most part user-friendly, but in my opinion not as much as is the CBDB. Additionally, the CBDB allows linking from their images, while the GCD does not.
I really like the Marvel Masterworks Resource Page. It's wonderful in that it tells consumers where to not only find high end reprints, but also contains listings of Essentials and trade paperbacks. There is some commentary, and numerous links. Perhaps the best part of the site is its inclusion of similar material (Archives, Showcase Presents) from the Distinguished Competition.
Lastly, I'd like to express my love for Treasury Comics! If this site isn't a love-in for a big slice of your childhood, then you didn't grow up in the Bronze Age! One of the best features are the front and back cover reproductions.