I've found the Microsoft Comfort Curve 3000 to be a good hybrid between a standard keyboard and a natural one. It has the curve that puts your wrists in the better posture, without the split so it's easy to get used to, and I like that the keys don't have as much travel so you don't have to press down as hard.

Unfortunately they seem to have discontinued it. I had picked up two a few years back for $20 each on Amazon, but now they're going for $100 on Amazon and eBay which makes no sense for a basic wired keyboard. It must be because of scarce supply and high demand.