http://www.google.com/ig<-- iGoogle. This is my home page. I don't generally look at it that much, to tell you the truth. Occasionally, I find an interesting news item in the sections that I've customized for myself. I generally find more stuff that interests me from links posted by friends on LJ or Facebook.
http://www.gmail.com/ <-- Gmail. I finally got around to consolidating my e-mail by having Gmail connect to my POP server and load my personal mail. One less tab to maintain.
http://my.ebay.com/ <-- My eBay. This gets checked regularly. I use Turbo Lister to actually make my listings, and if something sells, I get an e-mail. This is mainly used to check on bids and how many watchers an item has. I also use it when I actually process a sale. Because I have a store, I have something called "Selling Manager" integrated into this page. As a result, my My eBay page probably looks nothing like yours.
http://www.facebook.com/ <-- Facebook. Addicted. See previous post.
http://en.wikipedia.org/ <-- Wikipedia. This isn't actually the page I look at. The page I look at (and regularly reload) is my Watchlist. Some articles I monitor for changes because I want to be informed, such as Statewide opinion polling for the United States presidential election, 2008. Others I monitor for vandalism, such as Homophobia.
http://www.huffingtonpost.com/ <-- The Huffington Post. Maybe it's just because I'm watching the election so closely, but this has become my primary Internet news source. That may change after the election.
http://www.fivethirtyeight.com/ <-- FiveThirtyEight. If you're interested in politics, polling or statistics, this is the site for you. I'm totally hooked on it now. It has the smartest analyses of opinion polling I've ever seen. Again, after the election this will probably drop off my radar as a regular read.
http://webmail.uncp.edu/ <-- UNCP Webmail. Yeah, I have not integrated this account into Gmail and I doubt that I will. I sometimes overlook a message that goes into Gmail. It can just sort of fade into the huge list of stuff. Some of the e-mails I get here are too important to overlook.
http://blackboard.uncp.edu/ <-- UNCP Blackboard. I don't have any completely online classes this semester. I have one that is "hybrid online" and thus doesn't meet every week. I have another that uses Blackboard as a supplement.
http://www.angryzenmaster.com/ <-- Angry Zen Master. A fandom news site run by a good friend of mine. Our interests don't always overlap, but his insights and nose for geek news are invaluable. Please check it out.
These are the sites that I often keep in my browser tabs. If I don't keep them constantly loaded, I usually check each one at least daily if not every few hours. There's other stuff I pull up from time to time. I may write a couple more lists like this for other stuff I check out. I could probably write another post like this for webcomics, gaming sites and even political news sites.