Which microcontroller has good linux supported simulator?
There is good Linux support for many microcontrollers:

Atmel's AVRs are well supported, with the GCC compiler and avrdude for loading code. An Arduino makes a good development board for starting out.

Microchip's PICs are supported by MPLABX which provides compilers, IDE and code loading (using a PICkit).

The SDCC compiler supports 8051, Z80, HC08 and more.

ARM microcontrollers are well supported, with GCC and OpenOCD+GDB for JTAG loading/debugging. A good precompiled GCC toolchain comes from CodeSourcery.

TI's MSP430 microcontrollers are supported with GCC and mspdebug. See, http://hackaday.com/2010/08/11/how-to-launchpad-programming-with-linux/