r/ProductHunters is a subreddit for discussing products listed on Product Hunt. It's a good place to write a post to accompany your PH launch. r/ProductHunters has 7.5K member and is among the top 8% of subreddits by size.

BetaList is a large and well-known startup directory but it's also very selective. They review each submission before they decide whether to allow it on the platform. Your startup should be pre-launch or recently launched without substantial press coverage, needs a custom designed, decent-looking landing describing the product and a way for people to sign up.