Miceuz designed 2 open source single sided boards for Li Ion battery chargers. He used the MAX1555 and MCP73831 ICs as the charging controller, power is provided through USB. We especially like his battery holder rig.
For a long time I wanted to enter the 21st century by stopping using NiCad or NiMH batteries and upgrading to Lithium accumulators as they provide more power per volume and are cool in general. Constant flow of obsolete cell phones provides a nice source of reasonably high-performance batteries for free – I felt compelled to tap into this resource for my battery operated projects.