The correct pullup resistance for the I2C bus depends on the total capacitance on the bus and the frequency you want to operate the bus at.
The formula from the ATmega168 datasheet (which I believe comes from the official I2C spec) is --
Freq<100kHz===>Rmin=[Vcc?0.4V)/3mA],Rmax=1000ns/Cbus
Freq>100kHz===>Rmin=[Vcc?0.4V)/3mA],Rmax=300ns/Cbus
The Microchip 24LC256 specifies a maximum pin capacitance of 10pF (which is fairly typical). Count up the number of devices you have in parallel on the bus and use the formula above to calculate a range of values that will work.
For a bus freq > 100khz, with a bus Capacitance of 60pF, the Max Resistor value is 5k ohm.