Here are a few web sites that I definitely recommend:
Script Tutorials - resources for old handwriting and documents. Are you having trouble interpreting some of the old handwriting styles? This site, managed by the Center for Family History and Genealogy at Brigham Young University, offers tutorials on how to read those old documents - in German, Dutch, Italian, French, Spanish and Portuguese.
Virtual Calendars - I don't think that a research day goes by that I don't use this resource to identify dates referenced in newspapers. Do you find an obituary that says only that someone died "last Tuesday" and doesn't give the date? Start with the date of the newspaper, then go to this site and view the calendar for that month and year. You can determine what date was "last Tuesday."
Missouri Digital Heritage - if you are doing any research at all in Missouri, you need to check out this web site. It even has a treasure chest of digital versions of death certificates - all for free. It doesn't get much better than that. It was named as one of Family Tree Magazine's 101 best web sites in 2009.
The Minnesota Historical Society is another of my favorite sites. I've located death records and have been able to order copies of death certificates for a reasonable price.
Closer to home, the Nebraska State Historical Society just keeps getting better all the time. The site has a fantastic blog you must check out! The April 23, 2010 entry deals with the Great Sheedy Murder Trial of 1891, a story that has surfaced frequently in my research on great-grandfather Dan Kelly's brother-in-law, John Fitzgerald.
Which brings me around to THE BEST interactive history site I've encountered in recent memory, Gilded Age Plains City. I challenge you to click that link and spend anything less than an hour looking around, following links and interacting with the site.
Paula's Genealogical Eclectica - this is Paula Stuart-Warren's fantastic blog. A fantastic blog from a fantastic person. I was fortunate to spend Friday and yesterday soaking up all of Paula's tips and research ideas at the Nebraska State Genealogical Society convention. Her blog offers more great ideas, resources and just plain fun.
And - I'm pleased to announce that LongLostRelatives.net has been added to the GeneaBloggers blog! With more than 900 genealogy blogs identified on the site, you can't help but find information on a topic you are interested in!