Link building needs and strategy certainly vary from project to project, local to national, and keyword to keyword target. However, many foundational services are universal. I created the link building packages referenced below to compliment the on-site SEO service packages my previous marketing firm offered to clients. Phase 1 is tackling the fundamentals of on-site SEO. These link building services were often a Phase 2 of an SEO-focused online marketing strategy, and are good, general link building services for all clients, especially for clients with little to no link profile footprint. Also key to any link building campaign is really investigating the link profiles of top competitors and targeting those hubs to get links from as well.
These link building services include business directory sites, also more niche (in this example real estate-focused) as well as addressing more local and manual link building. Phase 3 would then get into social media and engagement of hub websites and social media leaders in that industry, as well as consistent creation of engaging content.
UPDATE: Link building today certainly involves leveraging social media to pass around great content, and working with online PR and tastemakers in a given industry.