Hi,
If you need controller for mass production then AT89C51 or AT89S52 are good as they are cheaper. You need to design hardware for loading program in it. Another option is, you can purchase loader from the market.
If you are a student and need few programs to be tested, you can use P89V51RD2 from Philips. You can use flash magic and boot the controller from serial port.
However, philips has stopped production of this controller. So this is not a good option. Many china made ICs are coming into market but its not goos in quality.