Committed line count is the measure I use. I find it is reasonably reliable. There is a big difference between a guy who is committing 15,000 lines a year and another who is committing 3,000 lines a year, and another who is committing 60,000 lines a year. Back in the day when I wrote a lot of code I maxed out at about 50,000 lines a year. The best programmers I have had personal experience with do about 200,000 lines a year. Guys that do that, the real burners, have to be very heads down and are hard to find. One guy I knew who was that level is a VP now and makes $500,000 a year.
You also have to take into account whitespace. There are some guys who put every brace on its own line, so you have to multiply by 0.8 to adjust for all the white space. In general, though, its just tweaking. Usually the good programmers will be producing double or triple or quadruple what the weakies do, so the whitespace doesn't really matter much in the long run.
The very first year I worked full time as a programmer I wrote an MS Access DB application. It took me the whole year to write it. After the whole thing was written and fully debugged and working, I did a line count. It was 400 lines of code. Nowadays, I could write that same application in a single day. Gives you some idea of the difference in skill. Nowadays, if I go all out, like its Goole Code Jam or something I can write about 1000 working/debugged lines a day, so in theory I could do 250,000 lines a year if I did nothing but program. Of course, I spend all my time now going to meetings, writing specs, winning new business and answering questions on SO, so I do a lot less than that.
Note that you have to take into account what phase the project is in. If the project is new, the line count will be a lot higher than an old project that is getting debugged. Also, as projects get big and hairy, the line count decreases somewhat.