Little computers? Who do people like?

I have two systems that I need to replace. One is my backup server, which runs FreeBSD and uses some USB attached drives. Really that could be done with anything that is like a Pi, except amd64/x86.

The other is my pfSense router. It is having some hardware issue, which isn't surprising, I pulled parts out of my scrap pile to make it. For that, I need something that can take an pcie card for my dual 10g network card. Does anyone have any ITX or smallish machines they like? Actual smallness doesn't matter so much as not being expensive.

How do people go about finding things these days? I used to use newegg, but mostly now it seems to be a trap of accidentally ordering parts from the moon. Amazon is fine if you know exactly what you want already. Pcpartspicker works well, if you are building a full system from parts (which I do for bigger machines) but I don't know where to get barebones boxes.