Subreddit Stats - Statistics for every subreddit.
Reddit List - Tracking the top 5000 subreddits
FrontPageMetrics - Daily updated statistics for every subreddit on Reddit. Top subreddits, new subreddits by date, all subreddits, trending subreddits, plus more Reddit stats
Unreadit - Weekly newsletters with the best Reddit content
RedStatz.com - Reddit Website Statistics
Beam for reddit - Discover and browse reddit on your iPhone