Ok. This is entirely speculation, but check this out.
Watch this trailer on the show's Facebook page, which says "to stay until the end of the credits on Tuesday. In true Marvel fashion, you never know what might happen."
Then at the end, they oddly zoom in on the head of the eagle in the logo then zooms out. It's now wearing an eyepatch. In other trailers for the show (I checked) the logo starts on the middle then zooms out. It's clear they want us to see this oddly placed eyepatch, which is a trademark of SHIELD Director, Nick Fury. My money is on Samuel L. Jackson making a cameo at the end.
I'm seriously surprised no bigger nerdy news sites have picked up on this. C'mon guys :P.
I'm secretly hoping they handle a story where, like in the comics, Fury runs into some kind of trouble and has to step down as SHIELD Director leaving the spot for Maria Hill to fill. They've already hinted at her becoming more of a regular on the show, especially since actress Cobie Smulders is more available after How I Met Your Mother ended, and that'd be a valid way of doing it. Meanwhile, they could do Fury's Secret Warriors stuff on the side if they want, having Samuel Jackson showing up in cameos for that, or even a full spin-off movie.
But, odds are more likely that he'll just show up to pat Coulson on the back and tell him he's doing a good job.
Or. Ooor. If Whedon is good, he'll have Fury be the one to level with Coulson on how they brought him back to life. That would be worth seeing too. In Avengers, he seemed to be the one hurt the most personally by Phil's passing.
"I got nothing for you. I lost my one good eye. Maybe I had that coming." -Nick Fury