I would look at least at three different companies about 8051.
If you need the fastest and best analog features, look at Silabs. They have a great variety with some exceptional features, outperforming any other 8-bit architecture I know with 100 MHz single cycle devices.
If you need more "standard parts" and top performance is not as important as low price, you want to look at Philips and Atmel.
While the standard 89C5xx or 89S5xx devices are very similar Atmel has a few advantages there. These devices are usually not really low cost.
Also have a look at the Philips LPC900 family which can compete in many things with the AVR but is still a 2-cycle 51 core.