Rena makes media that fits wonderfully in their XP filters. I get mine at petsmart, but you can probably get it at any other chain store as well. I have 3 of the XP filters for my tanks and love them. Here's what I put in my XP3:
Bottom Basket:
2 of the Foam30 pads on the bottom
2 of the Foam20 pads on the top
*I haven't changed these things in months...I always just clean them well when I do my filter maintenance and they're good as new.
Middle Basket:
Biological media
*This can be whatever you want, but personally I've had good luck with the ceramic rings
Top Basket:
More biological media in the bottom half
BioChem Zorb in the middle
Micro Filtration Pad on the top
*The biochem zorb is up to you as to weather you do or don't want to use carbon
Here's a link to the petsmart website:
http://www.petsmart.com/search/index...igkw=rena&sr=1