I'm planning on running my next project at 3.3v because the only batteries I have that are small enough are 3.7v Li-ion's. While the MCU should work fine directly from the battery, other components like the LCD and SD card might not be so happy with 3.7v rather than 3.3v. The obvious solution would be to use something like an lm1117 3.3v regulator, but they have >1v of dropout and would be useless. Is there anyway to regulate the battery to 3.3v without significant battery life losses due to dropout. Is there some sort of 3.3v regulator which can either step up or step down depending on input voltage. My project should consume less than 100mA absolute max.
You can get low dropout 3.3v regulators such as this one http://uk.farnell.com/texas-instruments/tlv70033ddct/ic-ldo-200ma-3-3v-5sot23/dp/1778230 (max dropoout voltage 175mV @ 200mA). However, if you are not looking for a well-regulated supply, then a simpler solution might be to use a Schottky rectifier diode in series with the 3.7v supply.
It certainly looks better than a lm1117, I think I'll give it a try.
I am about to embark on investigating the MCP1253 chips with a view to making a tiny 5V boost regulator board for Li-Ion batteries.
The chip is selectable for 3.3v or 5v output, and will operate from anything from 2.1V up to 5.5v - it's specifically designed for use with Li-Ion and Li-Poly batteries, and only needs a couple of capacitors to get it to work. It also has a "power good" open drain output so you can monitor your battery status too.
It's only available in MSOP though, so kind of tricky to work with if you're not used to tiny SMD chips.
FWIW, I have finished prototyping my MCP1253-33X50 chip based LiPo/Li-Ion battery regulators. They're pretty nice - very easy to work with (apart from the size).
http://digital-diy.com/forum/general-electronics/playing-with-the-mcp1253-33x50-t2296.html
There are available from Ebay "Adaptor" circuit boards that will allow one to solder a ssop or msop chip to a small PCB and have holes on a .1" (2.54mm) grid or pin spacing... For my old eyes and shaky hands a great deal as one can from several different sources get a number of different 'footprints' on a common board and the boards are scored such that it is easy to "Break away" the desired adapter and use only it.
Doc
Docedison:
There are available from Ebay "Adaptor" circuit boards that will allow one to solder a ssop or msop chip to a small PCB and have holes on a .1" (2.54mm) grid or pin spacing... For my old eyes and shaky hands a great deal as one can from several different sources get a number of different 'footprints' on a common board and the boards are scored such that it is easy to "Break away" the desired adapter and use only it.Doc
Handy. I tend to just etch my own, but then my eyesight hasn't yet succumbed to the ravages of old age 
I thought of using the MCP1253 as well at one point but I'm not sure if it's worth it. According to some Li-ion discharge curves I've looked at, and the fact that even an LDO will only work down to 3.5v (3.3v + 200mV regulator dropout), it seems like I might be pissing away a fair bit of the battery capacity using an LDO, whereas the MCP1253 would continue to boost the voltage up until the Li-ion is completely discharged.
Also, if I do decide to use the MCP1252/3, should I use the MCP1252 (650KHz switching) or the MCP1253 (1MHz)? the MCU will likely run from 16 - 32 MHz.
The MCP1252 has a switching frequency of 650 kHz, avoiding interference with sensitive IF bands. The MCP1253 has a switching frequency of 1 MHz and allows the use of smaller capacitors than the MCP1252, thus saving board space and cost.
So it's up to you. The 650MHz is better from an interference POV, but the 1MHz lets you use smaller caps.
I guess 650KHz would be the way to go, seeing as I don't know much about how to deal with noise and all the precautions necessary when running an MCU at high speed.
If it hasn't already been mentioned you could just run the 3.7v through a diode, most have a voltage drop of about 0.7v bringing your supply to 3v,
remember fully charged Lions' are 4.1v, Lipo's 4.2v