NeoPixels come in so many types. You can see all Adafruit's NeoPixel products here. I'll describe a few of the more commonly used types for wearables and cosplay, with pros and cons for each.

Strips

These are the most common type of NeoPixels. They come in a variety of widths and spacing. The most common are 30 lights/meter or 60 lights/meter, though you can also get the super-dense 144/m strip. 

The denser strips are more expensive, both in terms of how much they cost and also how much power they use -- your battery will last longer if you have dozens of LEDs instead of hundreds in your project.

Here's a quick video demonstrating the different densities.

Projects that Use NeoPixel Strips

• FireWalker Sneakers
• FloraBrella
• Wizard Staff
• Raver Bandolier
• Bunny Ears
• Wonder Woman Bracers

Dots

These are my favorite lights for cosplay applications. They are really tough! Each light is fully encased in plastic, so these light strands are really hard to break. I've even used them underwater. Adafruit sells them in 2" spacing or 4" spacing.

Projects that use NeoPixel Dots

• Fairy Crown
• Motion Reactive Tutu
• Sparkle Skirt
• Rainbow Hoodie
• Magic Light Bag

Rings & Pixels

Sometimes you want a small form-factor or just a few small lights. NeoPixel rings or pixels can be perfect for making light-up gadgets. They come in a variety of sizes: 12 pixel/ring, 16 pixel/ring, 24 pixel/ring, or a giant 60 pixel/ring size.

You can also get a 7-pixel NeoPixel Jewel which is perfect for necklaces or very small projects, or individual NeoPixels -- single pixels you can place exactly where you want.

These pixels are a bit more advanced to use and will require some soldering to get them working. 

These are also available in both RGB and RGBW versions.

Much more about rings here!

Projects that Use Rings & Pixels

• Ring Bracelet
• Superhero Power Gauntlet
• Kaleidoscope Eyes Goggles
• NeoPixel Jewel Necklace
• Color Touch Necklace
• Luminary Lanterns

Specialty

Here are a few other types of NeoPixel strip that exist!

• UV Blacklight Pixels: these do not show color, only UV purple, but they're still programmable in that you can change brightness and run animations on the strip. UV Parasol Project
• Side Light Pixels: Similar to the LED strips above, but laid out so the lights shine to the side. This is useful for projects that need to bend the strips in another way. LED Corset Project
• Neon-Look Strip: These strips are encased in a diffuser that make them look like neon, and they're really flexible and bendy.  Mickey Ears Project

Find out much more in the NeoPixel UberGuide.