There are a lot more than just these link-ups & groups but these are my favorites and the ones I use the most!
Bloggers Seeking Brands :: FB group where you can connect with different bloggers who share different opportunities
Bloggers Connect :: Google+ Community started by Dana from Wonder Forrest to connect with other bloggers
FBL: Fashion, Beauty, Lifestyle :: Another FB group, this one is more for connecting with bloggers and sharing your posts
Better Blogger Network :: is a community for bloggers to get help and get ideas to reach their goals
Bloglovin’ Collective :: Bloglovin’ link-up
Followers to Friends :: a link-up to help you make friends and not just gain more followers
Bloggers Coast to Coast :: Find bloggers that live close to you or at least in the same state (international bloggers are on the map too)