Selecting keywords for your content is perhaps the most significant decision you can make for search engine optimization (SEO). There are a variety of keyword services you can use to narrow down your focus. Whether you decide to do that, while simultaneously writing your content, is up to you. Many people prefer the freedom of just putting pen to paper initially, without the added pressure.

Picking keywords that match your content and have a reasonable chance of success in the SERPs is fundamental to a successful SEO strategy.

The first step in this process is gathering the most obvious search terms for your content.

There are various tools for doing this, and ill try to cover the most common ones for Google and Yahoo! Search.

This tool is designed for users of Google's Adwords programme. It provides a list of keywords and phrases strongly associated with your keyword/s and phrases, listed in order of relevance. If you advertise through Adwords, you'll have access to the bidding data as well, which will give you an idea of what's hot for your particular market.

This page is regularly updated and provides some interesting information on searching trends and patterns.

It's also possible to secure an extensive list of the most highly paid Google keywords and phrases, but keep in mind these lists are rarely up to date.

If you're really serious about leeching every possible advantage out of your keywords than you really need to invest in commercial keyword services such as Web CEO. These tools are particularly handy if you manage a large number of sites.

Web CEO is an outstanding tool that is scalable for different uses, either the lone webmaster or the corporate world. The most important aspect of these tools is there dynamic data on KEI.

"KEI" or keyword effectiveness index is a figure produced via an algorithm that compares search volume with the Pagerank of the top ranking sites, how many sites are using those keywords etc. Using the KEI can reveal some real gems for keyword's, and give a solid indication of the competition you can expect. Ideally you should aim for keywords or phrases with a KEI of no less than 10, although some keyword combinations are mandatory for different markets. I wouldn't make Peak SEO without targeting the term "search engine optimization" somewhere in my site.

Many website promotion and marketing strategists use Overture (now Yahoo! Search Marketing) alongside Adwords to supplement there promotion strategy. Overture ads appear on a number of search engine listings, including Yahoo! and MSN.

There are a number of freely accessible keyword services associated with Overture.

This free and simple tool allows you to search for keywords and phrases and get a total search count based on data from prior months. For instance if you do a search in August, you'll receive data from May. In the majority of stable markets this isn't a problem, but if your website is targeting a market with a relatively short shelf life, then you may need to find more up to date data.

It's a great tool for brainstorming alternatives keywords and phrases if your struggling to come up with a good list.

I have found two versions of this tool:

The international version is particularly handy if your site is split into sub domains for different countries. A keyword that works in one country doesn't necessarily get the same number of searches in another.

The Overture site has a number of other handy tools in the resource sector, including a view bids tool, ROI calculator and CPM Calculator.

Wordtracker is a commercial keyword suggestion tool. Its an outstanding resource for finding alternative keywords. Its primary use is for finding valuable keyword alternatives in PPC advertising. Wordtracker's suggestions are derived from a database of over 300 million keywords and phrases that people have used in the past 120 days. Therefore the keywords are based on the searching patterns of real life users.

There's certainly no shortage of keyword services on the net. The use of these tools and applying the keywords you discover will give you a terrific head start in the never ending race for quality traffic, and also help you to establish the best keywords to target for PPC advertising.