If you're looking for a quick, easy calculation, you can use:
ABV = (OG - FG)/.75
(and then multiply by 100 to get a percentage)
ABV = (OG - FG)*131
However, it's not a linear relationship, so there's a fair bit of error in both of those estimations but they'll get you within a half a percentage point of the actual value.
If you are concerned about accuracy, you'll need a messier formula, like the one you gave. Balling and DeClerk have good methods. There are also online calculators, like the one at Rooftop Brew. Or you could put one into a spreadsheet, and just enter your OG and FG there.
Again, if you want a simple formula, expect error.