I've been having an issue since Christmas on my 2002 SS (205K miles). It first happened while I was out shopping and it would crank, just not turn over. I called AAA. The guy came out checked it and said I needed a new battery because it was only putting out 19 Amps instead of the 700 it was supposed to. So I bought a new battery and a few days later, it happened again. It cranks, wouldn't fire up. It finally did after waiting about 10 minutes. This has happened a few times since then, after it sits, it will start right up. Saturday it started up and sputtered a little I gave it gas and it stopped sputtering and ran fine. That same thing happened one other time. Today it started, no issues.
2 years ago I had a new fuel pump and new spark plug & wires. Battery, starter and alternator all checked out fine. It's just like playing Russian Roulette now whenever I drive somewhere. I've had it looked at and checked out, and talked to a few people and no one has any idea what it could be. Typically whenever someone goes to look at it is when it is starting fine.
I did notice Saturday when it sputtered, was after I filled it up when it was almost empty. Could it be a dirty fuel filter & some crud in the tank getting stirred up?

 

wouldn't hurt to get a new fuel filter installed, and check the fuel pressure. It may be your fuel pump going intermittenlty, if it has a bad ground or is just dying slowly on you.
There is also a chance one of your coil's is dying, or you have a bad plug wire, the sputtering on start up still leads me to think more fuel related but aftermarket wires are not the best for our cars, so it could be that too.

Intermittent problems are the hardest and worst to diagnose unless you give it to the shop mechanic for a week to drive, I've had to do this in the past with a cavalier it would idle rough and hard to start, I told the guy it was the plug wires but they didn't believe me as everytime I had it to the shop it ran perfectly, but after driving it for a week the problem happened to him

 

When mine did that it was the MAS. It would start fine when cold but when I came back to it, at the Bodega or Walmart parking lot, it would start and die. Idle rough, then smooth out after about a min with my foot on the gas!
But Ohara is right. Fuel supply, plugs or wires. Also fuel pressure regulator.

 

Also check for vacuum leaks