I've never made my own hummus, although I think about it every time I buy some. I know it's insanely easy.

In any case, I have cooked with tahini. It's a paste kind of like peanut butter that's made from sesame seeds. You can probably find it in any health or whole foods store, as well as Middle Eastern markets; at my grocery store it's with the peanut/soy/almond/etc. butters.
If you're in a bind, you could make your own tahini or even leave it out, I guess. I just found a recipe for tahini online:
"It is very easy to make tahini at home. All you will need are some sesame seeds and olive oil. Coat a flat baking tray with olive oil and sprinkle the seeds. Bake in a 350 degree oven for 10 minutes. Sesame seeds burn quickly so keep an eye on them and flip them often during the 10 minutes.
Once lightly browned, remove from oven and place them in a blender to create your tahini paste." (from
http://vegweb.com/articles/anai-1059139077.shtml)