Cypress have recently introduced a new range of PSoC 4 development boards that are well worth a look Based on the 4100 and 4200 series of PSoC devices they feature a powerful Cortex M0 processor, include a programmer and are available from Farnell for less than £4 each. The PSoC Creator visual design software is free so you can get up and running with PSoC programming with very little outlay. There are also plenty of example programs plus extra user components available on the Cypress website.
The one weak point is the programming instructions that don’t really cover the USB connected development boards but assume you have a PSoC programmer. The solution to is use the following excellent Wiki that provides step-by-step instructions on USB bootloader programming: Bootloader Wiki.