Since the "Trash" is just another folder on the filesystem, from the Terminal you can send items to the trash instead of deleting them by simply issuing a mv file_or_folder_name ~/.Trash/ instead of using rm file_or_folder_name, which permanently deletes things.
[robg adds: Yes, this is a simple hint ... but if using rm in the Terminal makes you a bit apprehensive, mving those items to the trash instead will give you one more level of safety.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050911200335426