For: sketching/watercolor
Material type: Brush with a water dispenser in the handle.
Brand: Koi waterbrush-
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Where to purchase it: You shouldn't have to much trouble finding it in your local shop but it's also on sale on amazon.
Price comparing to other brands: avarage, a little under 10$
Pro: koi waterbrush is great when you're on the go. I use it to add a bit of volume and shade to my sketches, either by using a couple of watercolor crayons, or my col-erase (they have less pigment, but they still do a good job). Once you're done, just press the brush to get a couple of drops of water in the palm of your hand and wash it.
Con: Its material is synthetic and cheap, it's tip will get stained, but it still does a great job at what it's made for; a brush for quick watercolor sketches when you're away from home and all of your material.
Heck, here's an other one
For: sketching/3D
Material type: Software
Brand: Google sketchup
Where to purchase it:
google sketchup is free!
Pro: Sketchup is 3D for dummies... really, really unintelligent dummies. It's mostly used to do mockups and it's great to layout a scene. Just lay out some blocks and basic models, turn around your scene to find a good angle and voila! you've got a great base for your drawing. Other then giving you a chance to explore your scene before committing to a final camera view, it's also great when you want to do several drawings, in different angles, of the same place while keeping everything accurately in place.
Google sketchup also has an extensive library of 3D items you can use to layout your scene and lets you share your own model with the rest of the community.
Con: It's no where near as powerful as other 3D software.