Feeds Tamper

"Feeds Tamper provides a small plugin architecture for Feeds to modify data before it gets saved."

"[...]very necessarily for doing things like mapping taxonomy fields with multiple values. This is very difficult to do without Tamper" http://www.mediacurrent.com/blog/top-drupal-7-modules-winter-2014-edition

Feeds

"Import or aggregate data as nodes, users, taxonomy terms or simple database records."

Feeds Crawler

"Feeds Crawler is a Feeds fetcher plugin for paging through a site or a feed. It is useful for building powerful web scrapers using Feeds"

Migrate

This is by far the coolest and easiest way to do complex migrations. Once you learn this, you will be able to migrate just about anything into Drupal including old Drupal sites where using the core updater doesn't work right because of whatever complexity the old site had.

Soon, I'll be writing up an article on using this great module... For now, here's an article that I found which is a great read for anyone who may need to use this