Playstation writes:

As you already know, PSP Firmware Update v6.0 included a Digital Comics reader application that is accessible under the Extras icon on the XMB. Starting today, you can access hundreds of digital comics on Playstation Store, directly on the PSP or via Media Go (on the PC). You will notice a new “tab” for comics, next to the game and video tabs. The digital comics store is currently available in the U.S. only.

In the store, you’ll want to check out the “free comics” category, for a selection of comics that you can download for free. You’ll also find a great variety of titles from our partners at Marvel, IDW Publishing and Disney and more. See the launch list below.