I am currently looking for a candidate with the following spec, is there any
good recommendations?

8051/251 core supporting at least 512K byte program space via banking.
strong in i2c, at least 2 channels can either be configured as master or slave.
5 ports of IOs = 40 pins + external address/data bus.
good development support
relatively cheap
5V operation
24Mhz+ oscillator frequency.
good delivery time.

Rgds

Calvin