With Sony recently shutting down the store you once could access from your PSP it makes it very difficult to find some DLC, which will only run on Official Firmware. While others are just plain lost unless you find a Memory Stick with them saved on it.
Lets begin with one that bring you over 700 mini games in Hot Pixel which in itself is a weird title, with games more looking they belong on a Atari 2600 rather than a PSP.
As it turns out the official site is still up HERE just follow directions they are easy enough to install.
Next up is Wipeout Pure with it's 8 add ons which just about triples the numbers of tracks and vehicles available. Sadly it once was available but seemly no more.
Wipeout Pulse can be found here but only for European version of the game Here
I found a video that explains what was available