Marvel Chronology Project

Here are some links I use on a fairly regular basis when building chronologies:

The Unofficial Handbook of Marvel Comics Creators
-I usually use this to compare publication dates but it's useful for a bunch of other things.

Mike's Amazing World of Comics
-you can sort to see what all came out in a certain month and filter out different publishers.

Grand Comics Database
-just like it says, a great big database of comics.

mycomicshop.com
-the most user-friendly comic shop site I've seen. Cover scans for almost everything, and I usually use this to figure out what the different volumes of a series are. Also, pretty reasonable prices.

What reference sites does anyone else use?

I find marvel.wikia.com hugely helpful--it's very easy to jump from any one issue to a gallery of other issues released that month, and it's especially good for searching by criteria other than characters (settings, objects, etc.). I've also saved a copy of Supermegamonkey's entire Chronocomic site on my desktop, just to be prepared when it disappears someday.

My favorite thing on the Mike's Amazing World site is hidden away in "Downloads": the spreadsheet of all Marvel publications through 2009 (and, in some cases, through 2013 or so).

https://www.freewebs.com/marvelreprints/reprints.html is gone now, but can still be accessed via archive.org. It's useful for the superhero stuff, less so for horror/SF/Western/etc. reprints.

I also use http://marvel.wikia.com for character bios, as well as en.wikipedia.org

Oh, and this is a good site for locating obscure and international comic heros http://www.internationalhero.co.uk

I keep track of my collection with www.comicbookdb.com. I find it very helpful in finding comic information on particular issues, character appearances and such. A great resource.

www.atomicavenue.com is also a great resource for finding issues and information.