If you are cheap like me, try Krylon "Fusion" spraypaint. It is meant to be a primer and a topcoat, and is very resilient to wear. Click on the link below to view colors:
http://www.krylon.com/main/color_pro...rylon® Fusion
Fusion paints can be found at Canadian Tire, Wal-Mart and Michaels, for usually around $7 a can.
For "wear" effects, choose a colour thats darker than the transformers plastic, then wait for the paint to fully dry, next use a very fine grit of sandpaper and lightly sand the paint off of the toys edges.
As an alternative, or with black plastic, buy a small bottle of silver paint. I recommend Testors Acrylic Silver, but there are many brands of paint availible. Games Workshop paints are easy to find too, but they don't bond well to toys, so I would avoid them.
Anyway, to replicate wear and make details on the plastic visible, dip a small amount of silver paint onto a brush, than use a cloth to remove as much paint from the brush as you can. Now lightly brush the toy. You will begin to notice a small amount of silver paint on any edge, ridge or detail. The paint will gradually build up and create a highlight. The paint will not reach recessed areas and this lack of paint will create a shade (the effect works best on darker plastic). This painting technique is known as Drybrushing, and its very easy to do and achieve good looking results.
If you are feeling brave, experiment drybrushing with other colours and/or mix up new shades to better match the toy. I have seen Testors Paint sets at Michaels, Toys R Us, Zellers and Wal-Mart (although I believe Wal-Mart no longer sells them), and there are many to choose from. I recommend the Acrylic "Auto and Truck Colors" set;
http://www.testors.com/catalog_item.asp?itemNbr=2183
I found the above set at a Toys R Us for $13, and it has a good selection of colours, including Silver.
