[protoserge]

Off the top of my head, here are some printers:

Ultimaker
Makerbot
RepRap (Mendel, Prusa, Kossel, Rostock)
UP! (inventables.com has these)
Buccaneer
Stratasys


Things to look for: reliability, ease of maintenance, replacement of components, material costs.

Multi-color: This is not a requirement for most things. It will make your peices attractive, but at a huge increase in cost. There is a printer out there that can print any color on demand (I already forgot which company made it).

Extruders: There are two basic designs: direct-drive or Bowden. Many Bowden setups require fine-tuning to dial in the retraction rate. Direct-drive is basically a stepper motor on the print head which feeds directly into the hot end.

Hot end: This is the part that melts the plastic filament. Depending on how hot / how well the temperature is maintained, this will limit your material selection.

Heated bed: This is important for ABS plastic. It allows the first layer to adhere to the print surface and helps keep the next layers on target/aligned when printing up since the base layer has set well.

Materials: ABS, PLA, Polycarbonate, Nylon, Wood

Overhang:The overhang is basically how well the printer can print an "arch" without having to put support pillars under the arch.

Slicer/G-code: The software and firmware that convert the 3D model into paths, set the retract speed, print head acceleration and speed, as well as the thickness of the outermost wall (shell). Fine tuning in the printer software will result in huge variances in strength (more plastic is not always better), cost, weight, and durability.

Hopefully, this is some place to get started. There are so many printers out there you can easily find one. I would recommend against going for the cheapest ones out there and also against a large commercial printer (Stratasys) for a school setting. You may be able to get one with support and donated materials, so if it works out in your favor, there is no reason to immediately eliminate this. In the end, it needs to work or be repaired quickly. If you can get a sponsored service contract, this is something that might be worth looking into. However, expect to pay several thousand dollars for a repair call if there is no service contract. (And at that cost, you might as well just buy another Makerbot/Ultimaker/etc.)

You want one that will work, but also one that is maintainable, affordable, and cost-effective. I would not get an SLA printer due to the material costing $200+/liter. If it is for an engineering design class, why not have one that students and teachers can build, take apart, fix, and use. In fact, most of the videos are probably on YouTube already!