I think most of the Sense stuff are system level packages, so you'd either have to find a ROM that included them or monkey around with ADB to get put Sense back

I think most of the Sense stuff are system level packages, so you'd either have to find a ROM that included them or monkey around with ADB to get put Sense back on top. But if you want an stock Android experience that would seem to preclude Sense in large part. What the custom ROMs provide really depends on what phone you're on and the goal of the ROM. A lot of them are really nothing more than a new skin, but some make bigger tweaks. I've got the Vibrant, and there are custom ROMs for Froyo even though T-Mobile hasn't released an official ROM for that yet. There are also a number of 2.1 ROMs that have other customizations (overclocking, underclocking, changing battery behavior)