There are many mods out there for the Ps2!
If you're interested in being able to play burned discs as well as playing games from other regions then a modbo Modchip is the way to go!
You can find every diagram under the sun on Quade's Website
Here's a video of me installing a Modbo in a Ps2 slim 700xx V12 series
Personally, I prefer a softmodded fat Ps2. 
With a freemcboot Memory card, 2tb hard drive, Sata Network Adapter, and an Hdd to Usb dock, you can create a massive collection of Ps2 / Ps1 games via software called OPL. The setup is quite tedious and involved but once done, you'll be happy with the results.
I made a start to finish guide on this here. Grab some snacks because you're in a long haul.