My computer runs Debian, so I read debian-security-announce, which gets one email per updated package. Sample of messages from this year: https://lists.debian.org/debian-security-announce/2014/threa...

For Ubuntu:

https://lists.ubuntu.com/mailman/listinfo/ubuntu-security-an...

The subreddits r/netsec and r/crypto can be helpful

Follow infosec people on Twitter.

Who would you suggest?

There are plenty. Here are a few off the top of my head:

https://twitter.com/ErrataRob

https://twitter.com/mikko

https://twitter.com/thegrugq

https://twitter.com/r_netsec

https://twitter.com/0xabad1dea

https://twitter.com/agl__

https://twitter.com/dinodaizovi

@erratarob, @thegrugq, @mattblaze, @matthew_d_green, @swiftonsecurity

http://seclists.org/ is another great resource.