Do you know of natural supplements that increase focus and retention? i've read good things about l-tyrosine.

Many good options: B vitamins may help (esp. B12 if you're deficient). Phosphatidylserine, acetyl-l-carnitine, tyrosine, bacopa, vinpocetine, ashwagandha, gingko, rhodiola, dmae, hydergine and piracetam are all proven to help. There are entire books on this subject. A good article is at http://www.Smart-publications.Com/articles/be-smarter-think-faster-and-protect-your-brain-with-12-smart-nutrients.