Also curious to see some evidence. Tempted to give it a go, but I'm not about to spend $$ on something that isn't going to help.
I've found studies that do indicate it raises testosterone levels by ~42%. But this isn't significant in relation to muscle mass. I'll link.
However,
There are claims that L-aspartate is a special type of mineral transporter for cations, such as magnesium, into cells. Magnesium aspartate has not been found to be more biologically effective when compared with other magnesium salts. There are also claims that L-aspartate has ergogenic effects, that it enhances performance in both prolonged exercise and short intensive exercise. It is hypothesized that L-aspartate, especially the potassium magnesium aspartate salt, spares stores of muscle glycogen and/or promotes a faster rate of glycogen resynthesis during exercise. It has also been hypothesized that L-aspartate can enhance short intensive exercise by serving as a substrate for energy production in the Krebs cycle and for stimulating the purine nucleotide cycle. An animal study using injected aspartate failed to find any evidence of a glycogen-sparing effect or any ergogenic effects whatsoever. A more recent double-blind human study of male weight trainers similarly found aspartate supplementation to have no effect, and another study of the effect of aspartate on short intensive exercise again found no effect. /L-aspartate/
http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=83887#x321
Furthermore (it appears this might be a debunking post now I've gotten on this tack),
ZMA (Zinc monomethionine and aspartate and Magnesium Aspartate) is also apparently useless:
The major findings of this study was that dietary supplementation of a commercially available ZMA supplement resulted in a non-significant 12–17% increase in serum zinc levels but did not appear to effect anabolic or catabolic responses to resistance training, body composition, or training adaptations. These findings do not support contentions that ZMA supplementation during training increases muscle mass and/or enhances training adaptations.
No change in body composition or performance led to these results.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2129161/
I did find some studies however, supporting the use of creatine and beta-alanine supplementation,
http://www.ncbi.nlm.nih.gov/pubmed/17136944Creatine plus beta-alanine supplementation appeared to have the greatest effect on lean tissue accruement and body fat composition.
http://www.ncbi.nlm.nih.gov/pubmed/19083385In conclusion, despite a trend toward lower fatigue rates during 60 seconds of maximal exercise, 3 weeks of beta-alanine supplementation did not result in significant improvements in fatigue rates during high-intensity anaerobic exercise. However, higher training volumes and lower subjective feelings of fatigue in BA indicated that as duration of supplementation continued, the efficacy of beta-alanine supplementation in highly trained athletes became apparent.
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Personally, I only use whey protein and creatine, though I've been reading (which led to me looking at it as well) good things about beta-alanine. Happy to see something with zero or very minimal side effects that has a scientifically supported positive influence on muscle mass.
I think I'm in the camp of, diet+sleep with regular lifting being 99% of it, outside of other anabolic steroids.