Fluid is a simple application for the Mac that takes a web site and makes it appear to be a standalone application. It allows me to take my favorite web apps, such as GMail and Blogger, and add an icon for them in the icon bar and run them without first opening my web browser. Give fluid a try.
However, to get the most out of Fluid you need to utilize one important preference. Go to preferences, click advanced, and check "allow browsing to any URL." Many of the web apps I use require me to login. If you don't allow Fluid to go to a different URL, some apps will switch to a web browser to login, which defeats the whole purpose.