Thanks for all the responses, I've got a couple great options to experiment with!

Ok, so I am a huge fan of pesto and enjoying experimenting with different herb and nut combinations. Unfortunately, my girlfriend is highly allergic to tree nuts and has never eaten pesto. Can you imagine?

Well, anyways, I've considered using toasted pumpkin or sunflower seeds as a replacement, but have yet to actually conduct that test.

Does anyone know of any good, basic, pesto recipes that are completely nut free? Thanks!