not popular I guess; it's not even out yet, but the Pimoroni people are doing a GBA-like handheld kickstarter geared towards developing, called 32blit. Doesn't have all the cool bitmap, sprite, etc hardware I'm sure, but they try and give a pretty integrated environment. Also maybe geared a bit more towards beginners, but I really like the idea. And because it's modern hardware, you can just use all your standard tools. It's also got hardware debugging, looks like.