The best replacement for 8051 is avr.

The best alternatives to 8051 are rated as following:
★★★★★  avr
★★★★  pic
★★★  arm
★★★  8052
★★★  8086
★★  arduino
★  msp430
★  8031
★  atmega
★  8951
★  atmega328
★  80251
★  pic microcontroller
★  pic 16f877a
★  avr microcontroller
  z80
  cortex m0
  arm7
  arm processor
  atmel

Your alternative for 8051 is not listed? Suggest!
Speaking about 8051, one probably shouldn't forget about adc.

Other search terms related to 8051 and their ratings are:
★★★★★ adc
★★★ stepper motor
★★★ ethernet
★★ dac
★★ gsm
★ max232
★ spi
★ rtc
★ inbuilt adc
★ gsm modem
★ i2c interfacing
★ 128x64 glcd
external memory
7 segment display
8255
pwm
usb interface
eeprom
You have in mind a companion for 8051 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of 8051 in all years. Click on graph for more.
8051
avr
pic