What microcontroller can connect directly to a USB port?
I guess that by "two serial out ports" you mean one UART (since you also describe USB as 2 ports). Rocketmagmet indicates that many/most LED strings use SPI, but that will need at least 3 wires. Can you specify which protocol you need?     

In general Microchip has the lowest cost microcontrollers, also this time. And Microchip has many microcontrollers in DIL package as well, while many others have ditched that. May be important for DIY. The PIC18F13K50 


exists in both DIL-20 and SMT packages
works at 5 V (for interfacing with the LED strip)
is low cost at $2.5 (OK, that's relative, but USB able controllers are a bit more expensive than more basic types)   
has Enhanced USART for UART interface  
has an SPI interface in case you meant that    
has 25 mA source and sink I/O, so you can directly drive a couple of indicator LEDs if needed


Further reading
USB Generic Function on an Embedded Device, Microchip Application Note AN1166