What do you do when you visit a site and can't find the information that you're looking for OR if the information presented is stale and dull?
You click away, right?
That's why it's essential that you present useful, informative and entertaining content on your own site and basically, there are 6 ways to develop content for your site, which I've listed below in order of preference.
I've also listed recommended reading and tools below that will help you learn to write and source content on the web.
Cheers,

I've personally written 90% or more of the copy on all my sites. And yes, all that writing takes time, but when you're writing about things that are near and dear to your heart, it's not work - it's FUN! Better yet, strong personal endorsements ALWAYS convert better than merchant copy. Occassionally, when I've been in a hurry to 'get the word' out, I've used merchant copy. However, I always get permission to revise the copy first to avoid the potential of duplicate content penalties.
A writing tip...
If you think that your writing lacks luster or you find that it's a real grind, here's a tip... writing well really isn't that difficult. Can you talk? Can you tell a friend about a product or service that you like? If you can, then all you need to do is pretend that you're talking to a friend and and type what you would say to them.
To take it from there and improve your writing skills, consider training. "Make Your Content PreSELL" is a FREE ebook by Ken Evoy that is especially useful for affiliate marketers that teaches us how to write to pre-sell a product as opposed to trying to sell a product - which is the merchant's job. Get the book now or read my MYCPS review.
Another valuable book on this topic is Jim and Dallas Edwards' simple "Turn Words into Traffic" system that gives you a step-by-step action plan that shows you exactly how to write a 'KILLER' article on the web even if you think you can't write. You'll also see proof that Jim attracted 23,234 targeted visits in just 1 month from over 1,651 different sources just from his published articles.
If you really don't want to write, then hiring a ghostwriter is a great alternative.
Many webmasters build content for their sites quickly and cheaply using ghostwriters hired through Elance.
Some have articles written for as little as $2 a piece, but remember, you do get what you pay for. I suggest spending a minimum of $10 per article to get reasonable quality content --- and I've spent as much as $100 to have a magazine quality article written.
HATE to write? No problem! Private Label Rights are HOT!
Niche content packages and private label rights have become all the rage of late with webmasters who either hate to write or don't have the time to write.
Learn how to use and profit from private label rights, and check out this list of recommended "PLR" distributors.
Want to create your own ebook... easily? Then consider using a public domain work. Public domain works, eg. books, poems and articles have NO copyright protection. Anyone (me, you, anyone) can copy, modify and sell them. Better yet, you can even remove the original author's name and treat it as your own.
Moreover, once you modify a public domain work it becomes your property. The modified work receives an automatic copyright just like it would if it were an original work.
Public Domain Riches - Learn how to source public domain works to sell as your own material!
Public Domain GOLDMINE - Yanik Silver and Michael Holland have done the work for you. This package contains 35 different public domain along with all the market research, competitive analysis, keyword analysis, back-end affiliate revenue sources, and potential joint venture partners. Limited quantities available.
Using merchant copy is the option of last resort. Your visitors have seen that ad so many times before they get to your site, that when they see it again, they'll just click away. For a successful site, please use one of the options listed above.
It is possible to reprint articles posted on article directories such as GoArticles.com and EzineArticles.com provided you respect the author's copyright guidelines and restrictions for use.
Although I personally do recommend AGAINST using other authors' material because your site will bleed traffic through those author links, there's no harm in using them to build content and traffic initially.
Software such as Article Equalizer and Article Automator let you download hundreds of free articles to your computer, and even automatically format the pages around your site's template and then upload them to your site. Be warned however, PLEASE respect authors' guidelines and those of the article directory managers. Abuse of this software can hurt your bottom line.
Content and Article Marketing - In this section you'll find article distribution software, access to ghostwriters, article miners, headline creators and more. Includes "Article Announcer" which is article distribution software that puts your content on other webmasters sites and was listed in my "Best of 2005" newsletter.
Content Development Software - Find software that will help you create sales letters and headlines with a quick click of your mouse!
If you already develop your own content, and want to attract hoards of visitors and build backlinks to your web site by having your articles published on numerous article directories, I HIGHLY recommend that you check out Jason Potash's "Article Announcer" software.