The historical LIBOR -- or London InterBank Offered Rate -- interest rates can be extremely important to someone with adjustable rate mortgages, since many ARM rates are pegged to the popular index. Some loans peg their rates to an historic LIBOR average -- to the past six month's average, for example. And looking at the LIBOR's historical moves can give you sense for its recent volatility and trends.
The primary place to find the historical LIBOR interest rates is on the British Bankers' Association website. The BBA is the agency which determines, based on a a number of criteria, what the daily interest rate is and then distributes that information around the world through other agencies such as Bloomberg and Reuters (Moneyline Telerate). This information is used by some lenders to determine home mortgage interest rates and many other things.
A variety of financial websites, such as Moneyline.com or Bloomberg.com, carry regularly updated information on the LIBOR rate. However, the Libor interest rates posted on these sites may be as much as 24 hours old as they are not the originator of the information.
As you examine the historical LIBOR listings, look for trends -- has the rate trended down or up since the current economic cycle started? How has it performed in past cycles of economic recession and recovery? To the extent that it's possible to predict the future, this could give you a good feel for whether now is a good time to lock in an interest rate, or whether it might be better to go with a low-cost adjustable loan in an era of generally dropping rates.