I've just seen that Radiospares sells in my country the p89c51/52/54/58X2 chips.
I was looking to the features and could compare with the p89c66x I'm currently using
The only differences I've found are the Flash and RAM sizes which are respectively limited to 32K and 256 bytes for p89c58x2 and that the Flash isn't ISP and also that there is no hardware I2C implemented. Have I missed something else ?
yes, no PCA

The prices are very low compared to p89c66x.
It starts at 4.5 euros for a p89c21x2 to 9 euros for a p89c58x2 for unitary part.
Stephane, you will have to learn to buy a stick (24-30 pcs) that cost usually the same as 10 individual pieces. ($2.08 e.a. here when you buy a stick)

It means I should buy or design a parallel programming tool and my first question is which tool I could build to program these chips, the OTP versions and also 89c66x ? Which software to use ?
A parallel programming tool will always be useful so I should consider to have one. If you have a link to a good project, it will be the welcome.
Please, pretty please, do not build your own. I am under the impression that you make commercial products and if you start losing flash contents your careeer is over. Xeltek has quite a good reputation from the two owners/users here and is very reasonably priced. It seems (see RD2 programmer thread below) that my old favorite Needhams have got new management that is more interested in cutting cost than serving the customer - I would appreciete comments on this.
Next question is what is your feeling with the 89c51/52/54/58x2 familly ? Would you choose an other part for smaller appications ? I know that many people will say it depends on the application and they're right, but often we are working with two or three parts in the whole familly range to cover most of the applications.
The real question about the X2 vs the LPC is pins and memory. The LPCs have few pins and no ability for memory expansion. If I were to select 5 chips as all I had - and did not in any case need analog inputs or outputs - I would choose 89LPC932, 58X2, 668, 669 and a Cygnal part.

Stephane