There is no real second place in the list of the genealogically valuable U.S. state websites. The Washington State Digital Archives wins hands down, no contest. Unfortunately, although there are some other notable collections, most of the states have a miserable level of digital offerings. Currently, the State of Washington has preserved 165,412,383 records and made 64,505,776 records available as of November, 2015. They have also added 2,638,172 records in the past month. At the other end of the spectrum, most of the states make no attempt to systematically digitize their records and what they have preserved online is usually in a "Memory Project."
It would be an understatement to say that the process of digitizing state records and making the available to the public is highly politicized. Most state plead poverty on this subject, but it interesting that they always have enough money for more politically visible projects. It may not occur to many genealogical researchers that these state websites exist with millions of very valuable records. Even in states where there has been little effort made to digitize anything, there are still valuable online collections. It is further unfortunate that some states make a effort to monetize their collections and charge substantial fees for public records, even when they are already digitized. For example, the Arkansas History Commission has a collection of over 500,000 photographic images but only 13,000 of these have been digitized and made available online. However, there is no way to view the photos online.
Sometimes it is a matter of some considerable detective work to find what has been digitized and made available. For example, Wyoming has some very limited and partial databases online with links from the Wyoming State Archives. If you want a quick list and link to each of the state archive websites, I suggest the DigitalStateArchives.com website.
In many states, the digital collections are scattered into a variety of websites sponsored by different organizations. The most common repositories include state libraries and state historical societies. Many of the major state sponsored universities and colleges and a number of the private universities and other academic organizations also have extensive collections of state government related documents. We also need to remember that the online genealogical database programs have extensive state records. In addition, there are significant historical and genealogically significant collections in the public and private libraries around the country.
Many of the online state records are completely outside of the history/archive/library/museum circuit entirely. For example, in Arizona the Arizona Judicial Branch has a website entitled "Public Access to Court Information" and it has information about court cases from 153 out of 180 courts in Arizona. Online records are also maintained by counties and cities across the country. I would also point out that some of the land and property records are in digitized collections online, usually through a county recorder's office or the county treasurer.