Refractometers are about the only other reasonable alternative for the homebrewer. They are a little more expensive, but usually much easier to use. They only need a few drops of wort/beer to get a good measurement. Take note however, reading final gravity of your beer is not a one step operation. You need to do a little more math if you want to calculate ABV with only a refractometer. The nice thing is BeerSmith and probably other programs will do the math for you.
The flip side to all of this is that with the larger sample needed for the hydrometer, you have a good excuse to taste your wort/beer more often. Why dump those four oz. you need for the reading when you can drink it!
Just to clear this up some. When calculating ABV of your beer, you only need two number and one simple formula. Take the OG, subtract the FG, and divide by .00736. For example, a beer that starts at 1.050 and ends at 1.010 yields (1.050 - 1.010) / 0.00736 = 5.4% ABV.
When using a refractometer, you must adjust your final FG reading. This is because alcohol and sugar are present in the sample. Alcohol refracts differently than sugar. Therefore, your FG reading on a refractometer is NOT correct on its own. You must take into account the OG when reading the FG of the beer.
This makes it a little more complex than when you just use a hydrometer. There are plenty of sites that will explain and do the calculations for you. For example, a quick Google search for 'calculating abv with a refractometer' turned up this site (Onebeer.net) which seems to do a good job.
Of course, it wants the input in %Brix, which means you don't need the refractometer with both scales...
If you really want to know what the formulas are so you can do it yourself, then go to this site (Primetab).
OK. I swear I'm not drinking yet. But math mistake up above. I think that should have been 0.00763. But to simplify it a bit for everyone let's just do this instead.
ABV = (OG - FG) * 131
Now, some will say "Hey! That still isn't quite right!". I agree. The relationship between SG and ABV isn't really linear. High gravity brews have some other things to factor in. Other adjuncts and flavorings can change it all up. That magic number of 131 is just a compromise. Really is can vary anywhere from about 128 to about 135. But in the sake of keeping this simple for the homebrew audience, I think that is good enough.