Mainly scala devs or java performance people:

https://github.com/Atry

https://github.com/lihaoyi

https://github.com/davegurnell

https://github.com/nitsanw

https://github.com/mjpt777

https://github.com/milessabin

https://github.com/xeno-by

https://github.com/travisbrown

I follow a lot more but have chosen the n most interesting with a recency bias. In a few cases their blogs are way more active than github.

honourable mention for https://groups.google.com/forum/#!forum/mechanical-sympathy