Good call going with the sump! That opens up soooo many options for skimmers. There are two types of skimmers that I'd recommend: needle-wheel skimmers and high-pressure injection skimmers.
The needle-wheel skimmers (Euro Reef, Geosreef, ASM) are great in that they produce great skimmate with minimal noise and power consumption. One of these is probably your best bet for a 100 gallon tank. If your budget allows, the Euro Reef CS6-1 would probably be your best bet.
High-pressure injection skimmers (MRC, AquaC, Precision Marine, Aerofoamer, etc) also produce quality skimmate like the needle-wheels, but require a pressure-rated pump and can sometimes be noisy. Don't count any of these out, especially if you can find a good deal on one.