CP2102 modules for the USB, the modules are cheap, and work, what more do you want.
NB: Look for one which has the end pinout "DTR, RX, TX, VCC, CTS, GND" which is "the standard" (FTDI cable), that way you can just use a right angle female header on either it or the thing you're plugging it into and just plug em together. Some of the modules have slightly different pinouts which isn't so convenient needing jumper wires. If you do need to use the jumper wires that come with them, check the wires for end to end continuity before you start scratching your head trying to work out what's wrong, quality on those wires... variable at best.