Wisdomtree.com and Rydex.com and perhaps others have created etf(s) or etn(s) that provide us with the ability to buy currency.  They all work differently.  Morningstar, Yahoo/finance and other sites often guide you through the pluses and minuses of each product.  Remember, these are products.  The sites selling the product do have a lot of information, if you dig .  I think this is just a start.  Find articles that compare the products or evaluate the particular product you are considering.  In my opinion, these products do provide a means of being long or short a currency or a commodity but be careful.

For instance, many of the double longs or double shorts settle out each day.  So, long term trend does not matter.  These do not seem to be products for us.  Check and re-check before you buy.