Hopefully this helps someone...
Just bought some of this TIME RELEASED L-Arginine.
Dr. Mercola recommends time released L-Arginine because it keeps your levels of L-Arginine boosted for a longer period of time. It's supposed to keep the levels raised for 8 hours instead of just an hour or two from a normal pill...

I bought this at iherb dot com:
Doctor's Best, L-Arginine, 500 Mg 120 Bi-Layer Tablets
Sustained plus Immediate Release L-Arginine contains this conditionally essential amino acid in a bilayer tablet, with two tablets providing 500 mg of sustained release and 500 mg of immediate release L-arginine in a formula that allows for enhanced blood levels of this nutrient. Most supplemental L-arginine is quickly absorbed into circulation and is extremely efficiently metabolized, yielding only a short-lived boost to L-arginine levels. Sustained plus Immediate Release L-Arginine tablets are specifically manufactured to immediately increase blood levels of L-arginine and then to sustain this beneficial increase continuously over an 8-hour period.
L-arginine has been shown to support the cardiovascular system, promote vigorous heart function and enhance healthy circulation throughout the body through its conversion to nitric oxide. Research suggests L-arginine supplementation may also have positive benefits on athletic performance.