For deals:
Groupon
Gilt
all the many deal sites from Doodledeals to Fab.com to Jetsetter
For news:
Summify
News.me
LinkedIn
For discussion/comments:
Disqus
Wordpress
Facebook comments now support this
Smart apps for email:
Apple’s automagic appointment and phone number finders in iPhone Mail
Google’s “frequently emailed”
Xobni Smartr email synthesis