Scrapebox is the Ultimate Black Hat Bot or Grey Hat if you prefer. This is without a doubt the most powerful and best priced tool that you will find anywhere! It even has White Hat applications. There are almost too many functions to describe here, but here goes:

As the name implies, it is a scraper. This is also sometimes called an url harvester. This has many applications, but the most important being it will find the types of blogs that you need to post comments on and link back to your website.