I have an old Mac Pro that has been collecting dust for years. Today I bought an SSD and install Debian on the machine. It works flawlessly.
Further reading revealed that there is an active community around the classic mac pros and thanks to their modular nature they can be fully upgraded. People even upgrade the CPUs in this thing.
So if you like playing around with a PC like the old days, that is also Linux compatible, a Mac Pro 5,1 seems a good choice. AFAIK you can get it for cheap and a decent upgrade won’t break the bank.
Oh man, I gotta dust off my wife’s old 2009(?) MacBook now. I think the battery might be toast, but hopefully there’s enough of a cult following that I can find a replacement for that as well.
Update: 2007
Processor 065-6991 2.4GHz Intel Core 2 Duo Memory 065-6993 4GB 667 DDR2 SDRAM - 2x2GB Hard Drive 065-7452 250GB 5400RPM HDD Optical Drive 065-6998 SuperDrive 8X Display 065-7039 MacBook Pro 17-in Hi-Res GL WS