Tony Moffit had an interesting post last week about an artist who had priced their work per square inch, and had a gallery lower the price of their larger works. Tony correctly stated that the gallery had no right to force the artist to change the price of their work, but I disagreed with his statement that pricing by the square inch is correct. Since then, Clint Watson posted his own opinion on the Fine Art Views blog, and sparked a great discussion in the comments about pricing practices. If you haven't read either post, read both - they're great!
Pricing can be difficult for an artist, especially when starting out. It's easy to see the appeal of pricing work on a simply per square inch basis, but it results in very cheap small paintings and very expensive large paintings.
When I got accepted into my first gallery, they set my prices at something like $3/sq. in. I made next to nothing on my smaller pieces, but my larger work was at a good price point for an emerging artist at the time. My paintings started to sell faster than I could keep up (those were the days!), and the gallery and I quickly figured out that it was time for an adjustment. At the time, we increased my larger pieces by 10% and the smaller ones by up to 50% - in the end, my small paintings were priced much higher on a per square inch basis than my larger paintings, and they've stayed that way since. I keep track of this graphically because it helps me make sure that none of my prices are out of line. Here's what my pricing looks like for a wide range of sizes:

You can see that I range from about $9/sq. in. for a 6x8" painting, down to about $4/sq. in. for a 36x48" painting - not a small difference!
Nowadays, I set my own pricing, and adjust my prices when I feel a need based on demand. In the past, I've raised my prices 10-15% at the start of each year when I felt that I was having a hard time keeping up with my galleries, with an occasional bump in prices when I won awards or got magazine coverage. This year, I didn't raise my prices because I didn't feel that the current market warranted it, and I stand by that decision for now.
One thing I do to make sure my prices aren't unreasonable is to compare with a selection of other artists with similar resumes. I pick a handful of artists in this region who paint similar subject matter, show in the same tier of galleries, and have been in some of the same shows as I have, and I record their prices for a range of sizes. I put them all on a graph together just to make sure my prices are following the same trend, and aren't too far off in magnitude. Here's my graph for the last time I did this:

You can see that my prices tend to be on the low side compared with this group (I'm the bottom line), and I'm comfortable with that. A lot of my peers raised prices this year, so I'm left looking a bit cheaper than I used to be. My paintings are still selling well, so chances are I'll raise my prices a bit at the start of next year. In a market like we have now, I'm okay with being patient and just trying to do good work.