Classic -  The one and only classic Spider-Man look: Red & Blue, sometimes Red and Black costume with spider on front and back with webbing all around the red parts of the costume...This was Peter Parker's first costume after his wrestling costume he wore in Amazing Fantasy #15 and every time he went on to change his look, it wasn't long before he went back to the tried and true classics!...Here are some looks of the classic costumes:

Apart from artistic interpretations, the Classic Spider-Man costume has been relatively consistent looking throughout it's many years...The details most deviated from concerning his costume have been the webbing under his arms and the size and shape of his eyes in his mask.

About that webbing under his arms: Here is the Classic look by the great Spider-Man artist Steve Ditko...He displays much larger  webs under Spider-Man's arms that has changes from artist to artist and from time to time...Sometimes the webbing was smallish to not even present to the other extreme of it having a visual impact of spanning a wide area from his wrists to his waist.

Possibly the most Classic of the Classic poses displaying the Classic costume is the one featured on the cover of  Amazing Fantasy #15. Here is a rendition by John Byrne with a much smaller version of the webs under the arms.

Another minor variant on the Classic Red and Blue is when the Blue parts of the costume was replaced with Black parts...Some artists such as Erik Larsen and John Byrne have used this variation from time to time...Artistic tastes are the number one reason for changes in Spider-Man's costumes since the beginning.