One of the interesting things about modernist cooking is the use of unusual shapes to present food. There are many different shapes and types of molds, the ones you want to use will be based on the technique you are using and the presentation you are aiming for.
The molds are made of a variety of materials but many are made of non-stick silicon which is temperature resistant from -40 to 500 degrees F. Moreover, they can be reused up to 3,000 times.
For spherification one type of mold we recommend using is a hemispherical mold such as the World Cuisine Non-Stick Silicone Mold, Hemisphere, Mini (see above), which can make 24 hemispheres with a diameter of about 1 inch (25 mm). A slightly larger hemispherical mold is the Freshware 15-Cavity Mini Half Sphere Silicone Mold and Baking Pan with hemispheres of 1.6 inches (41 mm).
Another option for spherification is to use spherical molds such as the Hutzler Ice Ball Tray, 24 Balls.
We prefer using mold sizes under 1 inch (25 mm) or the spheres start to get really large; though if you want to spherify a whole soup that is served hot in a bowl you can always go for these huge Freshware 6-Cavity Half Sphere Silicone Mold and Baking Pan.
For gels, you have a lot more variety of shapes you can use. You can definitely use the above hemispherical or spherical molds for your gels, or even any flat-bottomed tupperware container.
Some of our favorite molds are the Freshware 24 Cavity Silicone Financier Pan, which create nice ½ inch (13 mm) deep rectangles (Right).
If you are looking for a variety of shapes this Freshware 30-Cavity Silicone Chocolate, Jelly and Candy Mold is a nice place to start (Left). It can be used to make 30 pieces in six different shapes. This flexible baking pan is made using high quality food-grade silicone with non-stick surface, which releases the pieces easily and cleans easily.Depending on what you would like your gels to look like there are a wide variety of molds by Freshware to choose from here.