First and foremost, the best way to maximize energy for workouts is through nutrition and sleep which are the the only way for your body to make real energy. I said REAL here because stimulants increase heartrate and alertness and thus perceived energy instead of real energy. Creatine actually does increase phosphocreatine stores which your body can use to create real energy, but food sources are probably more important... it's nerdy nitpicking
ANYWAY, creatine and caffeine are the two workout boosters you should start with. They are the most proven by both research and anecdote. Even better, they are the cheapest. Most commercial preworkout drinks rely on one or both of these to pack most of their punch.
For creatine, take 4-5 grams before and after workout. The best forms are creatine monohydrate (available from T-Nation) and creatine ethyl ester. You can try either or rotate both. Get the monohydrate in powdered form; it is tasteless in almost any drink. It may cause stomach problems if you don't take it with enough water. Creatine ethyl ester is nasty in water so get the pills. It is a little more expensive and there has been less research on it. It should cause less stomach problems in theory. I didn't have any problems with either. I prefer taking caffeine on occasion when I am feeling rundown and the boost will really benefit my workout, but the only real problem with taking it every time is building up a tolerance. I suppose other stimulants would be as beneficial, but I have no experience with them.
If you want to experiment with newer supplements and more exotic ingredients (note that the effects from these is much much less than creatine/caffeine), I would try beta alanine. It might give your skin the tingles which did happened to me. I hated it... some people don't mind it and some people love it. You could also try mental boosters. Find the thread about Brain Function boosters and they have a TON of different things in there you could mess around with. Alpha-GPC is one of the supps that has been discussed in there a couple times as a source of choline for your brain, but this is an area where I have much less experience and knowledge.
Maximizing testosterone naturally is much much less proven. If you are nutritionally deficient anywhere in your diet, then fixing that will up your natural test. You can try to get more monounsaturated fats in your diet, and that is supposed to help a little bit. Also, getting good rest will be good for your hormones. There are really no (non-hormonal) supplements that will raise your test significantly. Pro-hormones and steroids, both of which there are legal forms, can raise testosterone, but I take it from your post that type of supplement is out.