I would also love a thicker classic that would take 2.5" drives (and therefore support 500GB.) That, combined with an HDMI out dongle, would make it an awesome device for me. It's more than just storing lossless music, but also storing HD video, like supporting the "digital copy" that's included with Blu-Ray media.
Or, heck, I'd also like to see a hard-disk iPod touch. I've used folks iPhones with otterbox cases on it, that's about as thick and heavy as an iPod touch would be wiht a 1.8" HDD, and it would have to be much cheaper. Imagine a 160GB iPod touch? That's REALLY where more storage is needed, apps, videos, music, et al. I'm not saying get rid of the flash-based version, lots of folks will like that thin and light model (heck, they buy up those MacBook Air's like crazy don't they? They are willing to trade off a minor amount of CPU performance, a little bit of battery, and increase their cost [relatively speaking, $1,300 for the 13" base model], in order to have a super thin and light mac). I think that would be cool. Yeah it wouldn't be as "sexy" as the rest of the lineup (it would looks like a Zune, in other words), but it would be super functional.
-John