Fun fact: "tar xf FILENAME" will auto-detect the compression when extracting FILENAME. You don't actually need to specify "z" for gzip, "j" for bzip, etc.
That's GNU tar specific, though.
Works in modern bsdtar also, and as of a couple years ago they also added support for the "-a" flag to do the same thing when compressing.
tar xvf filename.tar
tar cvf filename.tar files
tar tvf filename.tar
I mean the joke is funny but if you use tar with any regularity how can you not remember the options?
I habitually use the verbose flag in any command that deals with a bunch of files.