Of course, the easiest corals of all are zoanthids, mushrooms and softies. I don't really like softies. The only softies I have in my tank are Kenya trees (and I SOOOO WISH I didn't have them), xenia and two leathers (a toadstool and a cabbage).
With mushrooms and zoanthids, the possibilities as far as color goes are endless. They come in every shape, size and color and are perfect for beginners.
Some of the best beginner corals are Euphyllia -- frogspawn, torch and hammer. They are pretty easy to keep and are very nice looking.
Bubble corals and fox corals are personal favorites of mine and are easy (I love LPS -- can you tell??).
Blastomussa are one of my favorite corals of all time, but they are usually relatively expensive, kind of hard to find nice specimens, and are not as easy as the other ones I listed above.