The Minecraft Wiki has more information on these effects.

• SPEED - called Speed
• SLOW - called Slowness
• FAST_DIGGING - called Haste
• SLOW_DIGGING - called Mining Fatigue
• INCREASE_DAMAGE - called Strength
• HEAL - called Instant Heal
• HARM - called Instant Damage
• JUMP - called Jump Boost
• CONFUSION - called Nausea
• REGENERATION - called Regeneration
• DAMAGE_RESISTANCE - called Resistance
• FIRE_RESISTANCE - called Fire Resistance
• WATER_BREATHING - called Water Breathing
• INVISIBILITY - called Invisibility, has no visible effect
• BLINDNESS - called Blindness
• NIGHT_VISION - called Night Vision, has no visible effect
• HUNGER - called Hunger
• WEAKNESS - called Weakness
• POISON - called Poison
• WITHER - Deals damage to an entity over time and gives the health to the shooter.

- '{entity}.addpotioneffect.{effect_type}.{duration},{amplifier}'
#use a comma between the duration and amplifier, or it will try to read a decimal

- '{entity}.addpotioneffect.{effect_type}'

Note: This doesn't seem to work yet, but that's Bukkit's fault. Adding a potion effect with 0 duration instead should work.

- 'if {entity}.haspotioneffect.{effect_type}': 'blah'

The Integer Variables for potion effects are of the following form:

'{entity}_potioneffect_{effect_type}_(duration|amplifier)'

These are not settable. If you want to set them, just add the corresponding potion effect again and it will replace the one already in effect.