This is a simple level translator with four channels in each direction, based on the On Semiconductor NLSV4T244. It is good from 1.4V to 4.5V (the part used is specified down to 0.9V but the specs at that low a supply voltage are poor; I'd consider very carefully before using it below 1.4V). There are no power sequencing requirements. The outputs can be tri-stated (all four in one direction as a group) under the control of an input. All inputs, including the active low output enables, are pulled down.

The schematic is here. Design files, using gEDA (gschem + pcb), are here. You can download the gerber files or order bare boards here.