Some of the previously mentioned MCU's have lots of "neat" features, not many of which really help the uninitiated in gaining knowledge about the MCU architecture, which is the goal stated by the original poster.

There's an old board, still available at www.nmiy.com, namely the NMIY-0031, which allows the on-board memory to be configured as external ROM, external RAM, or both. It also provides a few hardware hooks to enable the user to "play" with an HC44780-controlled LCD module, and a few other things. For about $30 it's worth a look.

As for the on-chip debug aids, I think it's most valuable for the beginner to learn how things work without such features before becoming entangled in the details associated with an ICE, or other debug aids not directly supported within the architecture.

I do find it annoying that most of the really low-cost boards save part of their cost by tying up the on-chip UART for benefit of the resident firmware, rather than using an external UART/BRG combination. Most people seem to have little difficulty living with that shortcoming, however.

RE