Too often I see a corporate site think they need a new URL to promote. Sometimes it does make sense but if you can, use a subdomain. Every new domain you create has to fight its way up Google. By using a subdomain, your new site will already be “trusted” by Google, start showing up in searches faster and will be ranked higher (especially if your main domain name or any other subdomains have good ranking). The subdomains help each other out, and you can make all your sites look similar and help build more content.
Google and Yahoo do this a lot. For example:
Instead of http://googlelabs.com they use http://labs.google.com
Instead of http://yahooweather.com they use http://weather.yahoo.com
You also cut your budget down by not registering more domain names, and if that new sites really takes off you wont have to worry about registering the .net or .org. I’ve even seen some people register the .info and other TLDs (which really makes no sense, unless your site is on the Top 100 on the internet or something).
Now when it comes to either using a SubDomain versus just a folder name, its up to you. A SubDomain is definately easier than anything longer than 1 folder. If you have another web application or service, it may be best to use the SubDomain. I think marketing a SubDomain is probably easier than a trailing folder. Although some non-web savy users will try to put a www. in front of your SubDomain. Yahoo pretty much gives an error page when someone does this and suggests the most likely page. Google will just forward them to the proper page without the www..
Some people still think the www. is still required, but it depends on how the web server is setup. I still come across a few sites that won’t work without it, which hurts making cases to users for not using typing it. Most people still think they need to type in http:// or when they delete the url in the address bar they delete everything up to that point. However most web browsers will put that in for you. Somethings things change slowly, but I’m digressing into another subject.