Bear in mind frames can slow a site down, and most search engines don't like frames. So use them only if they are really needed. I have seen so many web pages that really had no useful need for frames. A table could have easily produced the exact same effect. Remember, not everyone is on the latest, greatest browser or computer.
Frames do still crash older browsers or cause problems for older computers.
If you are a business catering to all users of all types then you may not want to limit who can access your site. Click here for more information about frames. A must read for anyone considering creating a business web site. Using plug-ins is also somewhat of a design problem. Don't get me wrong, those are great, but make sure you also create a site that doesn't use them.