That puffer is a small one, but I would watch out because they will turn on you in a minute. Don't be supprised to wake up one day with a chunk missing of your corals, or any slow/passive fish you add later. Ditto for the red coris. I am assumming he is a very small adult or a juvi. You do realize that this fish will grow to be about a foot long? As long as you are planning to upgrade to 120+ in the future you will be ok.
You have done a good job on fish selection so far, with all aggressive or semi-aggressive in there. Don't add anything passive, or it will be lunch for someone, as I am sure you know.
I would suggest a surgeon fish of some sort. If you are going to get a larger tank in the future, I would recomend what I have had good luck with, Pacific Blue Tang (aka palatte tang, nemo tang) and/or a purple tang. The Blue really get along well with other tangs and the purple does as well - and if you got them small enough you might be able to add both now, as I had my blue tang in a 55 for 3 years when he was a about 2 inches long, and put him in the 100gallon when he hit 4 inches with a 6 inch purple tang last year. BEWARE mixing any other tangs, however. Most don't play nice with others. Research them if you are planning on wanting more than one.
Even a small one will be able to defend itself from the rest of your tank's inhabitants. It will even be able to defend itself from you hand in the tank, so watch out, the tail spine thing hurts. Blue's grow REALLY slowly, I have had mine for over 5 years now and he is only 5 inches long - they grow about 3/4 inch a year. My purple is growing at 1 1/2 inches a year, however. Something to think about. A yellow tang, if alone, would be fine in your system.
That's what I would add, but here are some other safe ideas:
snowflake moray, small
reef-safe wrasse of any sort - six line, flashers, etc. Six line are tough fish
blenny - midas, canary, or bi-color would look nice
Just my 2 cents worth.
Good Luck,
David
