All you need is 1/2 cup of vinegar, 1/2 cup of Dawn detergent and one empty spray bottle.

 

Warm the vinegar in a microwave for about 90 seconds. Combine the vinegar and Dawn in the spray bottle.

 

Spray on your tub, shower and/or tile and let it sit for 1 or 2 hours.  Then, get that handy, dandy Mr. Clean Magic Eraser (or just a scrub sponge) and wipe clean.  This also works amazingly on glass shower doors!

 

Seriously, there is no other cleaner that money can buy that beats this!  I add a couple of drops of essential oil (lavender or Tea Tree) to the bottle to tame that vinegar smell.