Simple way to charge 5 x AA via USB - any off-the-shelf component for that?
Based on the comments in the question, if you want to use two AA Li-Ion  cells, charged from 5V USB input, you will need to boost the 5V up to 8.4V because each of the cells will need 4.2V charge voltage.  Furthermore, you will need a special charge management chip; you can't just run 8.4V across the two cells.

There are far fewer charge management chips for two cells that for a single cell, the MCP73213 is one.  There is a wider range of boost regulators that will take 5V in and can be configured to output 8.4V out; I chose the LMR62014.

Note that the maximum input you can expect from a USB port is 1A; according to the datasheet you will only get about 600 mA out from the boost regulator.  So charging 2 AA Li-Ion 2600 mA cells to full capacity at 0.2C will take some time.



For NiCd or NiMH batteries, you can use essentially the same circuit, substituting a suitable charge management IC for the MCP73213 for those chemistries such as the LT1511.