Jonathan - it depends on what you like the look of. You can check out LFS in your area and see what they carry. This will allow you to see the shapes of different types of live rock. Purchasing live rock locally may be a bit pricey. Ususally, buying online, the cost per pound is cheaper, however, remember to factor in shipping. Marshall Island live rock is really nice, Tonga, Kaelini, Figi, etc. You can also mix it up if you want. Were you thinking about curing the rock yourself (either in a separate tub, or in a new tank)? Check out the sponsors page, not only does Vivid (linked above) carry live rock, but Premium Aquatics, and others as well. See what everyone has available, and look at what will suit your needs the most.
Hope this helps