Choosing a Switchmode Converter for a Battery Powered Project

There are a number of ICs that will do these functions. I would go to the Maxim and Linear Technology sites. The downside is that most of these devices is that they are only in surface mount packages and a lot of them come in packages without leads (QFN, LGA).

A part like the LTC4088 is nice. It has an input for the battery, an input for the USB (or wall adapter) and a switching regulator.

You could also use separate ICs (but you are probably better off with a single). There is a device that Linear Tech calls a PowerPath controller (LTC4412) that performs the switchover function. You could add a MAX1555 Li-ion charger for a low cost charger and add the LTC4412. Also there are devices called "Ideal Diodes" that will perform switchover. These devices are FETs so you get a much lower voltage drop than a Schottky.

The best solution depends on a couple of things you haven't mentioned -- system current, battery capacity and recharge rates.

It's common in modern battery-powered audio electronics not to reference audio to 'true' ground, with +/- supply rails. Instead, you make an audio reference half way between ground and your voltage rail (often with a pair of resistors and a buffer of some kind). Then you arrange your audio signal to swing either side of this mid-rail reference - one tends to end up with quite a lot of series coupling capacitors to let you shift the DC point of the signal around.

Alternatively, if you don't like that (and there are reasons not to - getting the reference quiet enough and stiff enough can be a pain, as can the series caps, and at 3v3 you're fairly short of headroom once you've cut it in half), then a -ve rail can be produced using a charge-pump device like a MAX660 (there are lots of other sources for basically the same part) - that's a lot simpler than a full-up DC-DC converter.