For image rich sites, Pinterest, Instagram is recommended. If you have a specific niche for your business, you can try looking for communities or forums and gain engagement through interacting with them. Gooogle+ is also recommended for it is one of the fast growing online community with a lot of interesting features.
Major Sites would be Facebook, Twitter, Pinterest, Googleplus
Youtube for video marketing. Creat PDF and upload them to slideshare and issuu.
Share it to stumbleupon,reddit and other social bookmarking sites.
Do SEO with great keywords (creating quality backlinks for your website).
Have a social media (Facebook, Twitter, Gplus, Pinterest) and share it there.
Find niche social media sites where you can post your products like Chictopia an
Tumblr and Pinterest are two most effective social media site that can help me promote my brand. I also have accounts at behance.com and dribbble.com (communities for web designers) for my web design website.