I use the C8051Fxxx parts from Cygnal. They load via JTAG right from inside the Cygnal debugger. And then in addition to the easy FLASH handling you get a complete debug facility with run/stop control, single step and hardware breakpoints and ability to snapshot any registers or memory.

Michael Karas

PS. All Cygnal parts also support IAP capability so you can download and update flash from right within your application, or use flash space as data logging memory in additon to code space.

MJK