The AVR family from Atmel is very modern and getting more and more popular.
Texas new MSP430 family is also very modern and also getting popular.
Microchip have made the new PIC18F family, which have a more modern arcitechture than the old PIC16 family.
We use the AVR with the Atmel STK500 devlompment board for a MCU course at my engineering college. I think the AVR is very easy to use and it is very fast and very c friendly.
We use the CodeVisionAVR C compiler, it's quite cheap and good.
Compilers for PIC are more expensive and not as good as the ones for AVR.
I haven't tried to use the TI MSP430.
All three families are flash programable, like the ones you are used to.
Search elektroda for AVR vs. PIC and you will find some topics about these MCU's and MSP430.
If you want to learn more about the AVR then go to
www.avrfreaks.net, it's a very good starting point.