Seriphos by Interplexus is by far the most reasonably priced and effective form of phosphatdyl serine on the market. $19 for 100 as opposed to $30 for 60 for other types.
Relora is good too. I was using Seriphos for sleep and found it so strong for me (my cortisol isn't that high any more) that I'd wake up hung over with headaches. I now use Relora (Vitamin Shoppe brand, one or two capsules) when I have trouble sleeping along with melatonin and it really helps.