paulwhannel is right. I'll say a bit more, in case anyone cares for more details.
The icon in the Applications folder has the bulk of the product, so getting rid of it is usually good enough for practical purposes.
However, if you are compulsive and/or want to be tidy, you could use
File->Find (command-F) in the Finder and search for items with the name of your application. You will probably find small recordkeeping and settings (preference) files that you can also throw out. A proper application puts some of the resources it uses in well-defined Mac OS X locations, in addition to the locations inside the application itself.
For example, if you wanted to delete an application named
WhamoEdit, you could simply delete folder
Applications/WhamoEdit. But you might also delete files or folders named
Library/Application Support/WhamoEdit
Library/Preferences/...WhamoEdit...
Library/Receipts/WhamoEdit.pkg
(yourhomefolder)/Library/Application Support/WhamoEdit
(yourhomefolder)/Library/Preferences/...WhamoEdit...
For the software that comes with hardware devices (scanners, mice, etc.), there are still other standard locations for files. But whatever
File->Find finds is a candidate, as long as it isn't a file you created yourself, e.g.,
MyComplaintToTheMakerOfWhamoEdit.cwk.
Finally, many packages leave a receipt file (
Library/Receipts/WhamoEdit.pkg, as I mentioned above) that identifies resources used by the application. The
pkgInstall command can use this information to find and remove all files for an application. However, read the details at this link because it doesn't always work cleanly.