I don't really understand if your goal is to develop on an 8-bit MCU that has a USB peripheral, or just an 8-bit MCU dev board that has a built-in debugger (which connects over USB)?
If you want the latter, basically every MCU dev board uses a "native" USB connection for debugging... the classic Arduino UNO (and similar) boards are the only ones I can think of that don't have this.
If you want an MCU with a USB peripheral on it, continue reading:
http://www.silabs.com/products/mcu/8-bit/Pages/efm8-universal-bee-starter-kits.aspx
Couldn't agree more. The Silicon Labs EFM8 MCUs are really great little devices. Their dev boards are extremely cheap considering you get on-board JLink debugging, and you can connect external targets to it. Simplicity Studio, Silicon Labs' Eclipse-based IDE, has some great built-in code-gen tools to get your project going without getting in the way as much as Freescale/NXP's Processor Expert does.
Plus, the EFM8 parts are super cheap (I get my EFM8UB10s for 65 cents/piece @100 QTY), and the USB stuff requires zero external components. It's an 8051, though, so you get to do cute stuff related to that archaic architecture (different memory regions, constant SFRPAGE setting/retrieving, etc). Not so different from a PIC, but quite a bit different than the more modern AVR architecture. OK, I take that back; AVR can't run-time config a lot of stuff, so you have to use fuses, which feels really archaic to me.
Speaking of PIC, the Microchip PIC16F1454 (and similar) is a cute little MCU that I've used in several projects. Very similar to the EFM8 in terms of pricing/external component requirements. Microchip has really great USB demos that are self-documenting. Pretty hard to screw up.
Atmel's USB offerings are crap. You need external crystals, external USB resistors, and some parts don't even have built-in 3.3V regulators (!!). I fight with their USB stack whenever I'm forced to use their part.
More generally, I've developed a deep disdain for Atmel over the years. Their parts are expensive and don't compare well with other manufacturers in terms of peripherals/functionality/performance. I've had nothing but problems with Atmel's toolchain. I've jumped between several different computers over the years, and I've never had Atmel Studio actually work upon finishing installation. Tons of driver problems with the AVR Dragon (just last week, I had to re-sign the drivers using my own certs because Atmel couldn't be bothered to update their driver signing that expired in September... no joke).
Atmel made a lot more sense back in the day when they were the only vendor with free, easy-to-use tools. But these days, NXP/Freescale/SiLabs/Infineon/Cypress/ST have free, beautiful, standards-based cross-platform IDEs that aren't code-restricted. TI is still oddly code-restricted, but they have a ton of oddball options (free node-locked license with purchase of a dev board, etc). And all these manufacturers have low-cost debugging tools that work well. If you're eligible, the Segger J-Link EDU will target a lot of these parts, and I highly recommend it.
Some of these parts are 32-bit. It's funny that you talk about being "too stupid" to do 32-bit MCUs — these days, I feel way stupider when I poke around on 8-bit MCUs and have to remember all the weird #pragmas you have to do for ISRs, fuses, SFR pages, etc. All good 32-bit MCUs have nice HALs delivered either through run-time stuff, or through code-gen tools. I find them to be way more productive than 8-bit MCUs for everything but the most basic projects.
Just my two cents!