Subreddit Stats - Statistics for every subreddit.
Reddit List - Tracking the top 5000 subreddits
RedStatz.com - Reddit Website Statistics
Reddit Check - A tool to check if a URL is on Reddit and going viral
FrontPageMetrics - Daily updated statistics for every subreddit on Reddit. Top subreddits, new subreddits by date, all subreddits, trending subreddits, plus more Reddit stats
Orangered - A daily summary of your favorite subreddits