Making Toys with a 3D Printer
Perhaps the most alluring use of 3D printers is for recreational purposes, like making toys and decorative items. This is something such machines are both capable of and excel at, to the point that toy companies are using them to the same ends. Toys, after all, don't need to be anywhere near as durable as tools and so would require cheaper and more readily available materials to manufacture. Now you can have all the LEGO blocks you ever wanted, board games of all kinds, and limitless hordes of Army Men - but this time without the useless pointing guys clutching binoculars.
Which printer do I need?
Most toys and decorations, being small, can be made even on the smaller printers available, and objects which are larger than that can be made in parts and assembled afterwards. In any case, it would probably be reasonable to forgo the more expensive types of 3D printers and get something more manageable if you're aiming to make items for personal use. If you're looking to mass manufacture things for sale, it might be worth investing in a high-end 3D printer.
There are a number of desktop 3D printers currently available. On the pricey end of the scale is the Stratasys Mojo and uPrint SE series. The Mojo costs close to $10,000, with a 5" x 5" x 5" print area. Although the print area may seem rather small, Stratasys reportedly based these dimensions off surveys which indicated that 80% of current 3D printed parts fall within this size range, although whether this is enough for personal projects would be up to the individual to decide. The uPrint SE series range in price starting at $15,900 (printing materials included with purchase), have larger print areas (8" x 6" x 6" to 8" x 8" x 6") and, in the case of the uPrint SE Plus, can print in nine different colors, which may be a consideration if you do not have the opportunity or desire to paint your models with perfect precision. They're also fairly easy to figure out and begin using, but can also be a hassle to fix in case of problems (unless you're okay with having a technician come over to your house every time it breaks down), so may not be the ideal choice for a home.
In the slightly more affordable corner are the Ultimaker, MakerBot, and RepRap printers. The Ultimaker can be purchased for $1500 (disassembled)-$2200 (assembled), with an approximately 8" x 8" x 8" print area. MakerBot printers range from roughly $2000 to $2800 and printing areas between about 9" x 6" x 6" and 11" x 6" x 6". RepRap printers may vary in both price and print areas/capabilities (the basic parts kit starts at $520; fully assembled printers cost closer to $1200-$1800).
What materials should I use?
There aren't really any limitations on what sorts of thermoplastics to use in this case, so any ABS or PLA filament should do. Unless it's essential for the toy/object in question to be particularly durable, it's probably easier (and cheaper) to pass up the tougher stuff, like PC-ABS and ABSplus. If you do decide to go with higher-grade thermoplastics, make sure your printer is capable of using them.
Where do I get the designs?
Depending on what sort of objects you want to make, there are numerous websites with various 3D models which can be downloaded and used by 3D printers. Additionally, in some cases 3D modeling software can come in handy, for both making your own models and modifying existing ones.
Another option is to use a 3D scanner on a real object and create replicas of it.