Hello all,
during my minimalistic solar driven datalogging project (see here) I had to add additional EEPROM. Here is what I think is somehow the limit: four 24AA1025 I2C EEPROMs giving a total of 512KB memory space. This post in my blog shows the hardware setup and the way the memory is addressed through different I2C addresses. For having it more comfortably I added some code snipplets that show how to make one big chunk of memory with a linear address range out of it. Now addresses go continuously from 0 to 524,287 
If interested, have a look at:
Elektrix