The links provided below will link to the download areas. You should ensure that you select the correct version for PS3. These are usually appended with -powerpc+ps3.iso.
You should also note that there are often desktop and alternate versions available. The only difference being that the alternate iso's have a text console based installer rather than the graphical one (No, it's not scary). This can be a little faster during install but should not effect the final performance of Linux on your PS3.
The latest official release was:
Latest Development Release
The latest current development release is: