One way to be sure you are going to get something that meets Jim's criteria articulated above is to get a Toto.
You're obviously willing to spend north of $600 for a toilet, so you have some pretty-good-looking options in the Toto line, all of which will work and use readily-replaceable parts.
If you like the dual-flush, there's the Toto Aquia. However, I would caution that the dual-flush (.8 gal/1.6 gal) in any line isn't going to save you a material amount of water over the 1.28gpf Watersense toilets. You're likely to average that 1.28 either way, because you're using less water for liquids but more water for solids. That's why both kinds are eligible for the watersense program. And at least this guy isn't a huge fan of the washdown flush on most dual-flush toilets. Give me an Eco-Drake or a Dual-Cyclone anyday. But that's a personal preference.
If you like a modern look, there's the Carlyle II, the Aimes/Legato, the Lloyd, and, if you really want to impress your neighbors, the Ryohan. In the latter category, you really can't beat the Waza Miyabi series or the Neorest.
Just food for thought; the folks here evangelize for Toto simply because we know that they will work, that the workmanship will be excellent, and that you will be able to fix them when they need fixing.