Little late on this (long weekend,) but Mike Sampson at JoBlo scooped... well, the planet, as these things go... by posting a description (no photo) of Captain America's movie costume. Read his report, plus see some pretty accurate (according to Sampson) fan art mockups, HERE: http://www.joblo.com/index.php?id=32378
From Sampson's description, it sounds like they're using the "Ultimates" version of the WWII-era outfit ("present day" Ultimate Cap pretty-much looks like regular Cap) i.e. the "cap-colored" fatigues, but with the "Reborn"-style helmet/mask. Sounds manageable. Given this, I'd posit a 70-80% chance he'll wind up wearing a more "familiar" outfit in "Avengers."
What I'd like to know is if he'll also have "Ultimate Cap's" triangle-shield the whole time, or the round one. (In "Ultimates" he doesn't get the round one until unfreezing.)