Many sites link back and forth to each other simply because it makes good business sense to do so. If your web page provides good quality original information that is of value to Internet users you will naturally attract webmasters who will link to your pages as an extra service for their visitors.

You can also solicit one way inbound links for your website by

Participating in forum discussions
Blogs - use a weblog to promote your product and services
Articles - post articles in content distribution websites
Create a content syndication feed (RSS feed) and syndicate your material to other sites

Buying / Selling Text Links

Google and Yahoo both have the opinion that buying and selling text links lowers the overall value of links on the web and artificially influences SERP ratings. Read Matt Cutts article Text links and PageRank to learn how purchasing links can affect your websites search engine standings.

There are legitimate forms of link buying. Link trading, buying and selling that is designed to bring in real traffic has been used since the start of the web If this is what you are after, then buy links following the search engines link relevancy criteria.

Search engine algorithms use basically the same criteria to evaluate the value of one way links into your website as they do reciprocal links including

Comparing themes of the link source and link destination pages
Placement of links on the page (i.e. is it in body content, ad section, navigation area, etc.)
Relatedness of the two linked sites (are they in compatible industries?)

Buying or selling links is risky with the major search engines if they consider your link transaction to be spam your site will at the least be penalized in SERP pages

SEO MARKETING 101: SECTION FIVE: MONITOR, ANALYZE AND TWEAK YOUR PROMOTION Will show you how to easily measure your SEO marketing results and pinpoint problem areas with your website advertising, promotion and selling.