There are a couple of good ones out there. Of course, you have to remember that "all natural" is a very subjective term that's open to all kinds of interpretation. Most energy/nutrition bars will have some processed ingredients (like soy protein or whey protein), since it's difficult to boost the protein levels of these bars without them.

I recently reviewed the SoLo Low Glycemic Energy and Protein Bars, and really liked them. They are formulated to avoid spiking your blood sugar levels, which makes them better than a higher-GI bar at sustaining your energy.

Other options include the Fission Energy Bars, which were actually surprisingly good since I typically don't like fruit-based bars.

For a high protein bar, the Clif Builder bars are fantastic. I put it head-to-head against a couple other (not so natural) protein bars in a taste test and it was one of the top performers. If you want to read the tasters comments and ratings on all of the bars, check out: What's The Best Tasting Protein Bar? | Energy Bar and Protein Bar Reviews.

Best of luck!