Trying to green clean that shower? Consumer Reports says...

GreenerChoices.org, the eco-minded version of Consumer Reports. They test as report on supposedly "green" alternatives.

Cleaning up the shower? GreenerChoices says:  "Most 'green' shower cleaners haven’t wowed us. We found one decent choice by Green Works, called Green Works Natural Bathroom Cleaner, but it wasn’t great at removing mildew. Do-it-yourself cleaning recipes might be a better way to go."

Their recipe for a tub and tile cleaner.

Mix 1 2/3 cup baking soda, 1/2 cup liquid soap, and 1/2 cup water. Then, as the last step, add 2 tablespoons vinegar (if you add the vinegar too early it will react with the baking soda). Immediately apply, wipe, and scrub.

This is a variation on the common recipe for a tub and tile cleaner for your bathroom.

Other Recipes

EarthEasy recommends:

For simple cleaning, rub in baking soda with a damp sponge and rinse with fresh water. For tougher jobs, wipe surfaces with vinegar first and follow with baking soda as a scouring powder. (Vinegar can break down tile grout, so use sparingly.)

Green Joyment breaks it into two parts: 

Combine 2 cups of baking soda with enough water to make a smooth thick paste. Apply the paste to the tub or tile and let sit for 20-30 minutes. Scrub off with a soft rag in a circular motion. After the paste is removed, spray the tub or tile with a 50/50-vinegar and water rinse. The rinse will remove any residue and disinfect the area as well.

Someone on Associated Content has a little different take on it:

1 1/2 cups of white vinegar (only use white vinegar it works much better than apple cider or other flavored vinegars); 1 1/2 cups water; 3/4 cup of hydrogen peroxide (comes in a brown bottle you may already have some in your first aid kit). If you would like you can also add 40 to 50 drops of essential oil, for this recipe and oil that is naturally antiseptic such as lavender, orange, grapefruit or lemon will give the recipe added disinfecting power.

What are these recipes really telling us?
In your shower/tub you will basically have three kinds of cleaning to do: hard water spots, soap scum, and mold/mildew. What does this really amount to? Let's have a closer look at each problem.

Hard Water Spots: This is also known as limescale. The minerals in your water remain behind after the water evaporates off the tile and glass door. Lime is an alkaline substance (above 7 on the pH scale), so the best way to attack it is with something acidic. But hard water is also hard so you will need something abrasive to scrub with.

• Vinegar is a mildly acidic (below 7 on the pH scale), so it makes an excellent choice to attack the limescale. Lemon juice would also work, but I think white vinegar is a little more economical. However, lemon juice is actually more acidic, so if you have a tough problem you might want to go with the lemon or even lime juice.  Another way to getting more work out of your cleaner is to let it sit longer before wiping it up. So try leaving the vinegar/lemon juice to sit there for a five or ten minutes before wiping it up. 
• Baking Soda is a mild abrasive, so it should work well with the vinegar to give it some scrubbing power. However, baking soda is an alkaline and will neutralize the vinegar. You can see the reaction taking place as it bubbles up. Something like Bon Ami or Borax is a little more abrasive (and alkaline) and could be used instead of the baking soda. (But be careful with Bon Ami on glass shower doors.) All you need to do is make sure you don't let the vinegar and baking soda sit around mixed together for too long. 
• If I were using this vinegar/baking soda combination I would wipe or spray the vinegar around the shower/tub and let it sit for a few minutes. Then put some baking soda on a sponge (a little liquid soap can also help) and start to scrub. But be careful: vinegar is acidic and if you use it too much it might eventually eat away at the tile grout and caulking.

Soap Scum: Basically, soap scum, like limescale, is above 7 on the pH scale, so the same thing we said above about limescale applies here. Vinegar and baking soda make a good combination, along with some elbow grease.

Mold/Mildew: Tackling the mildew problem is a little more difficult. Vinegar, because it's an acid, can kill mildew but it's not always completely effective. Many sites will recommend using essential oils and tea tree oil because of their disinfectant qualities. But I would stay away from them for reasons mentioned here. It seems to me that a better solution is to use hydrogen peroxide along with the vinegar. However, like the vinegar and baking soda, I would not combine them beforehand.

My Recipe
So my final recommendation would be along these lines:

1. Put some white vinegar in a spray bottle and spray your shower with it.
2. Wait five minutes.
3. Put some hydrogen peroxide in a separate spray bottle and spray your shower with that too.
4. Wait another five minutes.
5. Mix together in a jar: one part baking soda and two parts borax.
6. Put a few drops of liquid soap on a sponge and sprinkle the baking soda/borax generously on the sponge then start to scrub your shower in a circular motion. Use some water if you need more moisture.
7. Rinse your shower out with water and wipe out any residue with a clean rag/sponge.