The WRT54 is still one of my favorite pieces of industrial design. Small case, ~~purple~~blue and grey, two antennas.
I bought it in anticipation of the Nintendo DS having WiFi capabilities, which I had never heard of before (I was like 13 or 14 then). Had to convince my parents to get broadband internet too.
Not a recent version, not from the last 10 years at least. They dropped even 8/32MB devices. On my Turris Omnia, the bare system with nothing else running takes about 70MB RAM, mostly because of kernel size. Linux itself isn't as light as it used to be.
The best you can do is put DD-WRT on it. AFAIK, they still use kernel v2.6 on devices this old.