I'd suggest getting a full panel of blood work done that measures A1C, plus lipids. Also, if you're looking to lose weight, take body measurements (a simple tape measure works just fine) - waist, hips, chest, arms, neck, calves. Weight is another valid measuring tool, but not the best to use as the sole measuring tool. You can use the body measurements to estimate body fat percentage or you can use other methods. So, in a nutshell:

1. blood lipids (cholesterol)
2. A1C (glucose)
3. body measurements (size)
4. body fat percentage
5. body weight

I'd use these, in this order of priority. :)

Depends on your goals, what's important to you, or why you would be switching to the paleo diet in the first place. If you are doing it to lose weight, weight, body fat percentage and BMI would be some good things to track. If you are doing it for health, cholesterol levels, resting heart rate, blood pressure and blood triglyceride levels. Or if you are a runner, measure how far you can run or how fast you can run a certain distance. If you are a weight lifter, measure how much weight you are lifting for each exercise and track the increase in weights. Or if you play a particular sport, just keep track of how well you are doing in each aspect of that sport I guess. You could track a number of things. I would figure out why you are switching and what your goals would be. We can't really set your goals for you ;)

For me it was taking a picture.

That and my jeans have told me that this is doing what I want. I didn't think of Jeans as a tracker at first, but for me they have been important. I just got size 12 jeans and I had been in size 18. I started eating paleo in October. The weight has come off too, but the jeans have more accurately tracked what is happening with my body :)

Once you know why you want to try paleo, then you can decide what to measure and track. I started out just wanting to lose weight, but I have learned a lot about how eating various foods can impact so many aspects of life.

For instance, I've started keeping track of joint issues, headaches, sleep habits, mood...so many things can be affected by diet, it's incredible.

Kurt Harris suggested these four were the best "predictors of mortality" (no particular order):

1. HBA1c
2. 25 (OH) D
3. HDL
4. Triglycerides

The original context is here, a comment on Stephan's blog.

Scroll down a little bit for Stephan's response: he also sees value in finding out LDL particle size (you know, little and dangerous versus big and fluffy). Based on the work of Ronald Krauss.

I agree with bkluffy. For example, I started are 2 weeks ago, and have since lost 14 lbs., over 10% of my goal weight loss. I had heard that most people who are on paleo and are heavy, they can expect to lose 10 lbs the first week, and then about 5 lbs. Every week until total weight loss goal has about 10 left to lose, then it seems to halt, and you should only be losing 1/2 to 1 lbs a week, because your body's running out of fat to burn, and is now building muscle, esp. If you exercise.

Could track amount of sleep and quality of sleep-might be interesting. Many feel the sleep better and need less sleep on paleo.

I think this is from Robb Wolf:

You're doing fine if you look, feel and perform good.

Maybe not all real, objectively measurable benchmarks, but good indicators none the less.

Good luck with your paleo journey!