Danios have lots of things going for them. They are very active, continually darting about the tank. They are inexpensive and easy to find in shops. They are very tough and could be used for cycling if you really needed to (although since I have gotten into plants I would never cycle a tank without some floating hornwort to absorb excess ammonia and thus help protect the fish during the cycle). They come in a variety of forms (the zebra is plain stripy, the leopard has spots instead of stripes, the gold danio is an albino zebra, and the pearl is kind of pearly colored) which are closely enough related that they school together. So you could have a bunch of danios that although they look different, will play together just fine.
Most of the barbs are too big for your tank, but the cherry barb would work well, and they are very pretty to boot.
If you wanted to treat them well, cories really wouldn't work. They like to have a sandy bottom, and they do best in groups. While you could easily keep a half dozen danios or cherry bars, cories are generally larger, and having a half dozen of them would use up alot of your available bioload. Also, they aren't algae eaters.
For algae eaters, I recommend shrimp (eg amano), nerite snails (for info on them, go to
http://applesnail.net/, click on Various in the left hand menu,
click on "Other freshwater snails", and go to the bottom of the page), or otocinclus (see
http://www.planetcatfish.com/cotm/1996_12.php).