To begin the process of removing an app, go to the home screen and tap "Market" (note: if your market shortcut has been removed, open the 'applications' tab and select market). Next, tap "my downloads." Once under your downloads, select the app you would like to delete, and click "uninstall." A confirmation screen will then come up; tap "ok." You will then be asked why you wish to uninstall the app. Once you select your reason, the app will be deleted.
NOTE: the app may still appear for a short time under "my downloads." This is so you can rate, comment on, or redownload the app. This does not mean the uninstallment was unsuccessful.