I have bought many I2C OLED displays from wide.hk on ebay. I LOVE these displays, the contrast is unreal and they are soooo thin and hardly take any current.
trouble was, no real libraries around or good code examples - ALL of the ones i found on the net are full of errors -- switching between CGROMS A,B,C is a big one, among other things -- 2 line vs 4 line, etc.
I sat down and read the SSD1311 Spec at least a dozen times until i thought I understood it completely. I have written an initialization sequence and some basic functions that, unchanged, will work on all three types of their I2C displays, the 2x16, 2x20, and the 4x20.
i use them on all of my projects, some of which can be seen on youtube in a seriously raw, unedited for the public video- using my iphone. look for 'nucloid99' on youtube to see the displays.
i'll try and post the sample code here, that has all the functions you need: INIT (a big one), set cursor, send a line, clear display, display a float, etc