I'm researching designing a custom PCB for a data logging project, and I need to include some kind of non-volatile storage. I really only need a couple megabytes of storage, so SD is probably overkill, but I presume that would be the cheapest option.

I see most of the micro-sd breakout boards have a chip on them, which I believe is a hex inverter. Why is that needed, and can a micro-SD slot pretty much be wired directly to the MCU, or is additional supporting components needed? Can anyone direct me to information on using an SD card without a breakout board?

As a separate question, is there some other option (very inexpensive) I can go with for up to a couple MB of non-volatile storage instead of SD? Speed is not a concern, and neither is the ability to remove the device, however very low cost would be preferable. So even a surface mount flash chip or something would be perfectly fine. Any recommendations?

Thanks!

The SD is a 3.3V device, il your mcu is 5V you need a "logic level converter", if your mcu is 3.3V you need nothing. Do not forget a clean alimentation: I use a condensator 0.1µF near to the SD connector .
I use a connector from Mouser 517-2908-05WB-MG. It is possible to solder wires directly on the SD card. The pinout is here:http://elm-chan.org/docs/mmc/mmc_e.html
For data flash there are examples in the Cookbook (http://developer.mbed.org/users/okini3939/notebook/extend-memory/)
Good luck

If low price is a key requirement and you don't need it removable then an SPI flash chip is probably easier and cheaper.

e.g. http://www.digikey.com/product-detail/en/S25FL208K0RMFI041/1274-1051-ND/3862736 will give you 1MB for $0.37 (picked purely for price).

A quick search for "SPI flash" shows that there are libraries already written for accessing a number of SPI flash devices, you may want to base your device selection on both price and what already has software support.

All you will need are a few wires direct to the appropriate mbed pins and if you want to be paranoid a small capacitor between power and ground as close as possible to the flash chip. Most mbeds have a 3.3V power output that you can use to power the chip.

One word of warning, flash chip sizes are normally listed in bits not bytes, make sure you don't end up with one that's 1/8th of the size you need ;-)