most apps need nothing more than a simple toss in the trash and an empty.
MS Office is one that DOES have an uninstaller and it's highly recommended to use it if you are tossing Office.
and most Mac OS apps can get tossed in the trashed, then pulled back out again with zero loss of usability.
still recommended that apps be in your applications folder tho, some actually look for themselves there and won't run or run right if they are not there.

macnuke is correct. Removing programs from your Mac is usually as simple as deleting the application file or, in the case of software with several appendix files, the software folder. The latter case typically occurs only with larger software packages that include helper files, plug-ins, modules, etc. that work with the main application.

Some programs store additional helper files in your home librarythe Library folder in the Home directory not the Library folder in the System folder. So if you delete a program also check your ~/Library/Application Support directory to see if there is a folder associated with the program you just removed and delete that also.

Lastly, most software will have a preference files stored in the Preferences folder (~/Library/Preferences); typically these will be .plist files. As Macs have never been limited to the cryptic DOS-like naming convention that Windows still employs for system, .dll, .ini, etc., files, the preference files for a given application should be clearly named. Considering the insignificant amount of space that these files take up, if you do not feel comfortable removing preference files you can simply leave them be, but if you accidentally erase a preference file for an application that you are still using, a new .plist file will be created automatically the next time you launch that app. In the worst case you only lose custom settings.

In all, removing applications from a Mac is far less of an issue that it is in Windows. Simply removing the application file/folder may leave some residuals, but unless you are in the habit of consistently installing and removing applications, the space these residual files take up is inconsequential; you will just have unused files on your main drive. Some others here may be able to suggest third-party options for cleaning up said residuals if that is a major concern for you.

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“Cannot run out of time. There is infinite time. You are finite. Zathras is finite. This is wrong tool.” 2.3GHz Power Mac G5/4GB/500GB HDD/OS X 10.4.11/30-inch ACD, 60GB iPod (Color)