If you are from one of the countries with which there is visa-waiver program up to 90 days (including US, UK, etc.) there is no problem if you want to come simply as a tourist. I assume you are OUTSIDE Japan now. And that you have left Japan some time ago, still with a visa sticker in it for one of the working visa types, and that you still have alien registration card.
Since you say you still have a valid visa, I assume that when you left Japan, you had a re-entry permit. If yes, upon entry they *might* ask you if you are coming back to work again. If you say no, you quit your job and now you're visiting as a tourist, they will cancel the previous visa, and give you a "temporary visitor" status stamp into your passport.
If you don't plan to come to Japan for any long period of time in the future, you might as well return the alien registration card, saying you are no longer a resident.