Mostly I was thinking of Reddit and Slashdot. On Reddit, even outside /r/hamradio and /r/amateurradio (why are there two? don't ask me!), I enjoy /r/electronics and /r/askelectronics, /r/rfelectronics, /r/rtlsdr, /r/carhacking, /r/arduino, /r/embedded, /r/engineering, /r/askengineers, /r/homelab, /r/datahoarder, /r/vintagecomputing, /r/askscience, /r/asksciencediscussion, and a few more.
I still enjoy Slashdot because, like HN, it's a single feed and gets me stuff I might not find in my regular subreddits.
I also read Arstechnica and The Register on a fairly regular basis, but not daily.
But honestly, my main firehose of news and ideas is IRC. I'm on 5 networks and about 25 channels, and I try to read all the scrollback in about half of those. There's lots of good stuff on Freenode and OFTC in particular, but I feel like this is one I should leave as an exercise to the reader. ;)
Not being snarky - I want to check them out!