Subreddit Stats - Statistics for every subreddit.
Reddit List - Tracking the top 5000 subreddits
RedStatz.com - Reddit Website Statistics
Upvoted - A news publication by reddit
FrontPageMetrics - Daily updated statistics for every subreddit on Reddit. Top subreddits, new subreddits by date, all subreddits, trending subreddits, plus more Reddit stats
Mailbrew - Automated email digests from Twitter, Reddit, YouTube & more