Do you have the dollar blues? If you've traveled abroad lately, you've felt some real pain. British pounds cost more than $2, and the euro is more than $1.40. Even our friendly neighbors to the north are hitting us hard, with the Canadian dollar worth more than its American counterpart for the first time in 30 years.

But if you've had the courage to invest overseas, you've probably gotten a big benefit from the falling dollar. As the dollar loses ground, assets valued in foreign currency get an automatic boost in value when measured in dollars. That's a big part of the reason why many international markets have dramatically outperformed U.S. stocks. For instance, the iShares MSCI EAFE ETF (NYSE:EFA), a broad measure of international stocks, is up 22.7% annually over the past five years. That far outpaces the 15.2% annual return of the S&P 500 over the same period.

Now, international investing doesn't automatically mean having to put your money in the stock market. As silly as it sounds, one of my best-performing assets over the past several years has been the Canadian currency I stashed away after my last big vacation. And thanks to the popularity of exchange-traded funds, even conservative investors can make investments in foreign currencies -- without going abroad to bring home a wad of multicolored cash.

Saving through ETFs
One series of ETFs gives investors a wide choice of foreign currencies to choose from. Offerings from the CurrencyShares Trusts track the value of eight different currencies, from the popular Euro Trust (NYSE:FXE) and Japanese Yen Trust (NYSE:FXY) to the Mexican Peso Trust (NYSE:FXM).

As with other ETFs, buying shares of currency ETFs is just like buying shares of stock. However, the price movements reflect the changing exchange rates among the currencies. In addition, you'll receive a monthly dividend that reflects the interest rates paid in that particular country. So for example, the Yen Trust pays a very small yield -- currently 0.23% -- because rates in Japan are very low. On the other hand, the Australian Dollar Trust (NYSE:FXA) pays nearly 6%.

CDs in foreign currency
In addition to these ETFs, Everbank offers certificates of deposit denominated in foreign currencies. With terms of three to 12 months, you earn a return based on exchange-rate changes and interest rates in your choice of more than a dozen foreign currencies.

You can also buy CDs that provide a mix of different currencies. For instance, one offering combines the British pound, Mexican peso, and Norwegian krone to reflect non-OPEC oil-producing countries.

Not for the meek
Buying these investments isn't as safe as putting your money in an FDIC-insured savings account -- not by a long shot. It's very common for these investments to lose principal; whenever the dollar strengthens, you can expect to see the value of your ETFs or CDs fall.

For the most part, these vehicles are designed to give speculators an easy way to make bets on the direction of exchange rates. But as a way to hedge some of your currency risk, these funds aren't a bad way to diversify the cash portion of your portfolio. If you're a typical U.S. investor, you not only have most of your assets in dollar-denominated investments, but you also earn a salary in dollars. Although they're not without risk, keeping some of your assets in international investments can make you money if the dollar continues to be weak.

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Fool contributor Dan Caplinger looks for as much diversification as he can get. He owns shares of the Euro, Yen, and Canadian Dollar Trust. The Fool's disclosure policy works around the world.