On a laptop, use an application such as to constantly scan for open networks. I've even found signals from coffee shops or cafes that reach into a lobby, but you might have to walk outside the hotel to find a suitable signal.
Just leave inSSIDer running, and it'll scan for networks. If you find one that doesn't require a password to log in--keep an eye in the Security column--connect through the Networking and Sharing Center. (You can often reach this directly by right-clicking a Wi-Fi or network icon in the System Tray.)
You can also often buy similar software for a Wi-Fi-capable mobile phone. Many utilities serve the same purpose on an iPhone, for example, such as . And once you locate a good network, you can return with the laptop.
Keep an eye on conspicuously named networks, too, such as ones that share the name of a restaurant. Even if there's a password, you might be able to sign-in for the cost of a cup of coffee.
But remember that these connections--even your paid hotel Wi-Fi--are insecure. Consider and other data with encryption.