While I'm at it, let me talk about a very popular fish: clowns. I hate to deliver bad news, but Disney's sweet Nemo would be a real unusual clownfish. I very much enjoy watching them. I had a mated pair of clarkii who wanted my whole tank: I finally traded them in as a breeding pair to someone who had a very big tank for them---because they were terrifying my 4" long damsels and wreaking havoc in the tank, moving rock they didn't approve of and otherwise biting, killing corals they didn't want near their nem, and generally being pains. Cute, oh, Yes. But you really need to know what clownfish are, and they're not Disney plush toys. They're smart, bitey, pushy, and while I love them, I can say I've served my time having clown fish and am very glad they went on to have many, many, many, many, many babies. I saw a barrel of their offspring once, and it was a 32 g tub with enough clownfish to have supplied half the southwest.

So don't be downhearted: I think everybody should have their go at clowns. I'm just not sure they're a great 'first fish," and I'm very certain that maroons aren't---. Experienced handlers only and very determined clown-keepers, for those guys.
Sizes.
skunk clowns, get probably up to 3".
http://www.reefhotspot.com/store/product_info.php?cPath=21_30&products_id=104.
They're the mildest disposition of the lot, IMHO.
The percs:
http://www.reefhotspot.com/store/product_info.php?cPath=21_30&products_id=1025
About 3" and fairly moderate in disposition.
The ocellaris.
http://www.reefhotspot.com/store/product_info.php?cPath=21_30&products_id=2744
About like the perculas.
The clarkii.
teeth, disposition; will bite the hand that feeds them, and will claim half your 100g tank. about 4".
http://www.reefhotspot.com/store/product_info.php?cPath=21_30&products_id=935
the tomato
Now we're into serious aggression. fight a buzzsaw. Or you.
"bold disposition" is an understatement. I've put my hand in a tank with my piranha. The red clowns worry me.
http://www.reefhotspot.com/store/product_info.php?cPath=21_30&products_id=2249. Beautiful but onery, and headed for large 4-5".
Maroons.
these go up to 5" inches, possibly more, and are a living terror to their tankmates. Have been known to grab intruding fish and stuff them in their anemone.
http://www.reefhotspot.com/store/product_info.php?cPath=21_30&products_id=789. They're magnificent to watch, but a mated pair want their own BIG tank, and you do not put your hand in without gloves.

Not kidding here.