Is this for your 125?
How ling has the tank been set up?
How much Live Rock do you have?
Kaudern's Cardinal (Pterapogon kauderni), also known as the Banggai Cardinalfish or Spotted Cardinalfish (Sphaeramia nematoptera) also known as Pajama Cardinal are nice additions in pairs.
A Yellow tang, Foxface lo or onespot) would a nikce splash of yellow in the tank.
You really have a lot of choices in a large tank depending on your water parameters, filtration, water change schedule, etc.
I usually go to liveaquaria.com
to check on fish that I'm interested in, then I do a google search for more iniformation.
The last step would be to post here stating everything about your tank and what you want to add. People who have or had a similar fish can then tell you their experience with the fish.
At a minimum you should post:
How many gallons is the tank?
How long has it been up and running with fish?
Filtration both mechanical and biological?
Describe the lighting units (type bulbs, total wattage).
What are the current water parameters? Ammonia, nitrite, nitrate, pH, salinity, temp, calcium and alkalinity. Please post numbers of results.
What else is in the tank (livestock and equipment)?