No one becomes a great investor in a vacuum. These tools help you learn from peers and see what "the street" is saying about the stocks you care about.
Seeking Alpha - Seeking Alpha is a large online investing community. Professional and amateur investors and analysts share new investing ideas, discuss the latest news, debate the merits of stocks etc. There are free and premium tiers available.
Commonstock - Commonstock is an online investing community that amplifies insights from top investors, backed by the performance and portfolio in their linked brokerage accounts.
Value Investors Club - Value Investors Club is an invite-only online community for discussing stock ideas.
SumZero - SumZero is an online community of 16,000+ buy-side professionals. Members are pre-screened before being admitted.
StockTwits - StockTwits is a social media platform designed for sharing ideas between investors, traders, and entrepreneurs.
Also see "Top SEC filing and Red Flag Services". For even more tools and resources, see "The complete list of free & paid investment research tools".