Your category for inbound links must include those links that creates traffic around your website. Here is the lists of the major categories which you need to search for.
On Site. Always use keywords on each link on your website that directs to another website.
Directories. Directory links that are fee based
Subscribers. This refers to the related industry search engine in which your website information was requested.
Your Partners: Reciprocal linking to trade and professional associations, business partners and resellers.
Media. Use this medium for publishing useful articles, site reviews and press releases that will help the promotion and marketing of your website.
Ideally, most of the links in your website would possibly fall in about two to five categories. If majority of you inbound links seem to be outside or not belonging on those categories, then do a request to web administrators asking them the removal of those links to your page. It will be useless to keep a link that are not relevant or connected to your site.
Anything or whatever you choose to do, always avoid the what you call LINK BUYING. This are schemes which are promoted and can be found mostly on different sites on the internet. This schemes promises you to have hundreds of inbound links in a very short period of time. Search engines are very sensitive to this kind of techniques. If they go over your website at a certain month and if during that time you have about 100 links then after a month you will then be having about a thousand inbound links, be watchful about this or else you are risking your website from being removed permanently in the search engines.