I recently ran across a post on the projector section of diyaudio which, in turn, linked another post on an aquarium site which spelled out the different ballast/bulb compatibilities better than I'd seen it done before, so I figured I'd paste the info here. I have edited out some info irrelevant to projector use (mainly on 175w and mercury vapor bulbs) and have added some additional info found elsewhere for the 150w ballasts/bulbs. Please post any corrections.

Obviously, this is really only helpful for U.S. builders, as I believe no one else uses ANSI codes.

150w:
Double-ended HQI: ANSI M81 or electronic
Singled-ended: ANSI M102 or electronic
Short-arc ceramics: ANSI M142 (with 1.8 amps input)

250w:
Probe start: ANSI: M58, core, capacitor
Pulse start: ANSI: M138, core, capacitor, ignitor
HQI: ANSI: M80, core, capacitor, ignitor
EYE: ANSI: H37, core, capacitor, actually a mercury vapor ballast
Electronic: ANSI: universal

400w:
Probe start: ANSI: M59, core, capacitor (LL bulb works with these)
Pulse start: ANSI: M135, core, capacitor, ignitor
Electronic: ANSI: universal
S51 High Pressure Sodium ballast will run the Ushio UHI-S400DD, Philips Mastercolor Ceramic, and the Eye Cera if it is ever released.

Additional notes: (quoted from original thread)
probe start will run american bulbs with ignitors built into the bulbs like coralife and venture bulbs. some german and euro bulbs will run fine on these, but without an ignitor, the bulb struggles to light and bulb life may be decreased. also reliabilty goes down.

pulse start will run the german/euro bulbs (ushio, AB, radium, etc.) these bulbs don't have built in ignitors, so the ballast has the ignitor wired into the circuit. the ignitor provides the high voltages needed to fire the bulb. you can run probe start bulbs on these ballasts, but the two ignitors may try to fight each other and possibly cause a fire.

HQI ballasts are similar to pulse starts in their wiring and ability to run bulbs. the output is a little higher which is meant to run the double-ended bulbs (commonly called HQI bulbs). people run mogul bulbs on these and they run a little hotter and brighter because they are being overdriven. this in turn shortens the life of the bulbs.

EYE ballasts are mercury vapor ballasts. they are similar to a probe start ballast, but the only bulb you can run on these are Iwasaki 6500K bulbs (because these are actually MV bulbs, not MH bulbs like most think). the ballast will damage MH bulbs if you try to run one on it.

Electronic. ahhh, the great electronics. these will run any bulb at the rated wattage: probe start, pulse start, iwasakis, DE (double ended-HQI). if you think you might change your mind in the future, get an electronic. you can change bulbs to whatever you want and not have to worry about the ballast being the wrong type. electronics run cooler (a magnetic MH ballast will burn your hand if you touch the coil after it's been running for awhile). they also use less energy.