Another display in my collection is a Newhaven NHD-1.69-160128UGC3 RGB OLED display. I'm basing this work on my SSD1322 project.
4-Wire SPI (software and 8-bit HW) works, but non-8-bit SPI in hardware is not possible on the Mega and this chipset doesn't support 3-Wire SPI. 16 bit color works but 18 bit doesn't.
This should work for various SEPS525 displays (e.g., others in the Newhaven series using this chipset).
Setup: I used an Arduino Mega 2560 with the latest Arduino 1.5.8 IDE. I used a 74LVC245 for voltage translaton. The display was wired per the serial specs for it, with the level shifted Arduino pins going to the corresponding board pins. The reference voltage for the '245 and the display was 3.3V. (Never apply 5V directly to this display!)
Hardware note: The CS line is particularly susceptible to noise in hardware SPI mode... touching my finger to it and a few nearby pins seemed to make the problem go away - a tiny 10 pF cap between the CS line (after the level shifter) and ground cleared that problem up. (This didn't happen with my SSD1322 device.) However, I didn't ground every single unused line and it turns out pin 11 (D15) and pin 12 (D16) are really noisy during hardware SPI writes (no idea why they aren't as noisy during bit-banged SPI). Grounding pin 11 and pin 12 (and at least one of the main grounds like pin 1) makes this display work even when the pins are touched (no extra capacitor necessay).
Update: The best option is to just ground all the unused pins.
I recently got a Newhaven NHD-1.69-160128ASC3 RGB OLED display to try out with my Particle Photon - it worked rather painlessly, despite foregoing the Arduino optimizations in the initial iteration. I prefer this board - it's far more robust in this sort of environment and is better engineered for a hobbyist.
Further reading:
Specifications: http://www.newhavendisplay.com/specs/NHD-1.69-160128UGC3.pdf Specifications: http://www.newhavendisplay.com/specs/NHD-1.69-160128ASC3.pdf
Chipset app notes: http://www.newhavendisplay.com/app_notes/SEPS525.pdf
A grateful nod to Tomaž Šolc's OLED library, particularly for helping me understand some of the esoteric settings this display uses (that aren't documented well in the data sheets).