First off without going into spoilers, it was pretty good. Not the best Marvel movie of the summer (That one goes to X-Men) but the action sequences were good and the acting was surprisingly good as well (Tommy Lee Jones stands out and Chris Evans shows he can carry a movie on his own). Now for the information, the scene that was filmed in NY with Chris Evans and Samuel Jackson is not an after credits scene, it is shown as the last scene in the movie. It has Captain America waking up on a bed in a white in a room listening to a Mets baseball game and a girl that looks similar to Peggy Carter walks in to the room and he asks her “Where am I?” Realizing the baseball game he was listening to was from 1941 he gets out of the bed and two guards walk into the room and try to calm him down but he pushes them though a wall and breaks out of the room into a warehouse and runs out of the warehouse onto times square. A squad of special forces surround him then Nick Fury says “At ease solider.” He tells him they were trying to adjust him to his new area and he has been sleeping for 70 years and asks Captain America if he has some where else to be. Captain America says ” I am late for a date.” (That line will make more sense when you see the movie.”
Now for the after-credits it's not a scene, it's a trailer for Avengers. It does not show much and its more screen flashes then anything else. It starts with Chris Evans punching a bag in the gym and eventually punches the bag so hard it breaks. Nick Fury walks in and asks him “If he is having trouble sleeping and tells him he has a mission for him. The screen says Next Summer. It shows quick shots of the the Avengers in costume around (with the exception of the Hulk) and Nick Fury tells them he has a mission for them. It then shows all of the characters one by one and ends with Thor throwing his hammer. Then Says May 2012 on the screen. It does not show the Hulk at all in the trailer just a brief shot of Mark Ruffalo. As I said the trailer was short, showing quick shots of the characters but it looked like Loki was in one of the scenes shown, but overall I cannot wait for next summer. Until then go see Captain America!
In addition to what's mentioned above, regarding The Avengers trailer, SHH user ComicGeek-86 adds on:
"When Loki is shown, it looks as if he's being escorted by guards (Shield? Something else? Not sure) And also, Tony Stark passes by Thor, patting him on the bicep and saying "That's quite the swinging arm you got going there" (Or something to this effect. Can't remember the exact wordage)
UPDATE: SHH have posted their description of The Avengers trailer, revealing a few tidbits not mentioned above.
We see quick snippets of Tony Stark and Steve Rogers, Loki being escorted in "handcuffs" by SHIELD. After that it's a long shot of Thor rocking a new outfit reminiscent of his Ultimate garb (sleeveless) in front of some roundtable of SHIELD. Then basically after that it's shots of action scenes - Cap in some sorta battlefield, Black Widow doing some flips and throwing darts, Hawkeye [and] a shot of Bruce Banner taking off his glasses.