This is probably the best overall measure of the dollar's value relative to other currencies. The Fed calculates this using inflation rates from a large group of major U.S. trading partners. The dollar bounced from its all-time lows starting last summer, but it is still below its long-term average. As I've noted before, the dollar's bounce was roughly coincident with the collapse of most commodity prices. This phenomenon is variously referred to as the unwinding of the carry trade, or a global deleveraging process.
Although the dollar has come up from its lows, I don't consider that the dollar is in a strengthening mode, because a) the Fed is not even close to trying to boost the dollar's fundamental value by tightening the supply of dollars (and indeed the Fed seems to be doing everything within its power to increase the supply of dollars), and b) the dollar, as well as all major currencies except the yen, is at or close to all-time lows relative to gold.