Those were the Haradrim, men from the lands South of Mordor, who have become allied with Sauron and are marching to do battle for Mordor.
and who were the similar looking guys going into Mordor (that almost discovered frodo and pippin Sam? [Hair])
Those are called Easterlings... Also a race of men marching to the aid of Sauron.
PJ didn't expand on them too much, and Tolkien didn't go to a lot of detail explaining those races to us... A little, but I don't think PJ felt we needed to know, yet. More will undoubtedly be explained about both of them in RoTK. For now, all we need to know is that they are working for the bad guy.
the flamboyant looking elf with the big nose that leads the elf army to the fortress towards the end of the movie?
That was Haldir, the very snooty elf that the Fellowship met when they entered Lothlorien in the first movie, remember him now?