Gluatamine. It's the least sexy supplement, but every time look into it, I find out something else amazing about it. Let alone the numerous health benefits, volumizing and recovery aid, it also permiates your brain and turns into glutamic acid which will imrove your focus and make sure you get a good work out (it's great for that combined with the BCAA's and taurine you're thinking about). I would chose it over arganine any day.
Since your thinking about BCAAs and Taurine, and some people have mentioned Citruline Malate, you could get Scivation Xtend. It's got all of those, and although the dose of Glutamine is only 2.5g, that's still enough to get you focused. It tatses great too (no I don't work for Scivation:lol: ).