Mike,
Jim H. has info on the Boca Chica area, but the best fishing (and a large charter fleet)is off the East Coast at Bavaro, near Punta Cana.
Although charter boats are few, off the mouth of Samana Bay lies a deep bank that has produced large striking fish, including several 400+ pounds blue marlin that I eventually lost after good fights. I also boated an Atlantic sailfish close to 40 pounds, one of the largest I've ever caught.
Just around the corner and to the north west of Cabo Cabron you will find big dolphin (fish), kings and wahoo, although the best wahoo fishing is up in the NW corner of the country off Monte Cristi.
Hope this helps. Catch 'em up.