Here's a cool method I read about in Hideo Kamimoto's book Electric Guitar Setups. You need to have a digital or analog multimeter so that you can measure the resistance as described. You want to have a pair of test leads with a clip built into the end. Also, a capo is handy for holding the strings down in the position where you're getting the buzz.

* Clip one of the leads onto the string that's giving you a buzz, between the nut and a tuner.
* Put the capo at the position where you're getting the buzz. Example: If you get a buzz on the 3rd string when you fret it at the 8th fret, place the capo at the 8th fret of the 3rd string. The multimeter lead would be connected to the 3rd string between the nut and the tuner.
* Sit in your normal playing position, and play to reproduce the buzz. While doing so, hold the other lead from the multimeter on the fret you want to test. Anywhere that the string is buzzing against a fret, it will complete the circuit and you will get a reading. You may find that the string is actually buzzing against several frets. For example, using the previous example, if you put the second lead on the 12th fret of the 3rd string while striking the 3rd string, and you get a reading, then it's buzzing on the 12th fret. Strike the string in your normal playing fashion so's not to introduce false results - obviously, if you strike the string really hard, it will vibrate much stronger and buzz against frets it wouldn't normally buzz against.
* Finally, repeat this procedure for each individual string that you're getting buzzing on.

If you are getting buzzing, it could be due to a high fret, and it's possible that just tweaking the bridge saddle for that particular string may be enough to solve the problem. If not, you may want to bring it to a reputable luthier or repair shop and have it investigated further. Here's a couple of excellent links to help you diagnose fret buzzes: