NXP LPC1343 GPIO questions
The table contains the minimal value for IOH but not the maximal value. What is that supposed to mean?


Note that this is the "current with voltage drop less than 0.4 Volts". The Minimum value is the only one of interest in this case - this has to be taken into account for the following logic. The maximum cannot be higher than the short circuit current, btw.


  user manual tells in 7.3.2 (pg89) that for LPC1343 max output voltage is 2.6V


The chapter talks about the weak Pullup resistors in input mode. See Fig. 9 just above that chapter.


  Why are no HIGH level output current values for I2C pins in datasheet


I²C is open-drain, pulling the bus lines high is forbidden except for the external pullup resistors.


  I did not find the value of pull-up and pulldown resistors anywhere in the documents... why is that? 


They are not resistors. In Fig. 9 you don't see resistors but transistors as weak pullup/pulldown. You cannot make "real" resistors efficiently on silicon chips.

Also look closer at the currents:

Ipd_min:  10µA at 5 V = 500 kOhm pulldown resistor
Ipd_max: 150µA at 5 V =  33,3 kOhm pulldown resistor 


That would not look nice in a datasheet - especially when compared to common 1% resistors.