Smoke on the Water is not a Guitar riff, it's a keyboard. My personal favourite is this (Basically Kashmir by Zep) But for me me it has to be "Layla" for most "Recognisable" to the General public.
Best guitar into IMO - Incubus - Kiss to Send Us Off or Aqueous Transmission Best non guiter intro - Placebo - Running Up That Hill
whole lot of love---zep smoke on the water----purple burn----purple or a personal fav of mine---20th century boy---t-rex
Just had a look over my favourites playlist, nothing better to do, these are the type of thing: Clash - London Calling Cult - She Sells Sanctuary Kinks - You Really Got Me Motorhead - Ace Of Spades Sex Pistols - Pretty Vacant Smiths - How Soon Is Now Not neccessarily the best songs ever but if you remember the game show "Name That Tune", these are name that tune in one (obviously a clue is given too...)