Geocontrol isn't actually the best (IMO) for creating explicit, large-scale terrain features. It's also a bit pricey. If you need free, Wilbur is a surprisingly good option. For more money, take a look at Leveller. World Machine and L3DT are other options, no worse than Geocontrol for your needs, but probably not as good as more "painterly" editors like Wilbur and Leveller.
- Oshyan