The Sony Xperia X3 is supposed to be Android based, and looks like a very serious piece of kit: 4" OLED screen, twice the screen resolution and twice the processor GHz of the Hero, plus an 8MP camera with a flash. Quite when it'll be out is anyone's guess - some time between now and Christmas seems like safe bet.
The Samsung Galaxy (i7500) is more similar to the Hero, and should be out very soon, I believe.
Link:
Samsung I7500 preview: First look - GSMArena.com
I haven't had much of a chance to play with the Hero, and I'm new to the smartphone game

but it seemed pretty slick - about as close as you can get to an iPhone without actually being an iPhone (although if that's what you're looking for then maybe you should actually get an iPhone!

). The screen supports multi-touch, and it's all very nicely intergrated and designed to be operated with a finger rather than a stylus.