My answer is divided in 2 parts
- when a corporeal creature wants to attack an incorporeal and ignore the 50% miss chance
- when a incorporeal creature wants to attack a corporeal and ignore the 50% miss chance
1 PART) When a corporeal creature wants to attack an incorporeal
The incorporeal subtipe from "Rule compendium" 64 states the following:
An incorporeal creature can be harmed only by other incorporeal creatures, magic weapons or creatures that strike as magic weapons, and spells, spell-like abilities, or supernatural abilities. Even when hit by spells (including touch spells) or magic weapons, an incorporeal creature has a 50% chance to ignore any damage from a corporeal source
continues
except for positive energy, negative energy, force effects such as magic missile, or attacks made with ghost touch weapons.
So by description of incorporeal subtype the following are ways to ignore the 50% miss chance:
By Type of Spells: Incorporeals are affected without miss chance by enchants:
- positive energy
- negative energy
- force effects (such as magic missile)
By Weapons
- attacks made with ghost touch weapons
By Feat
- Transdimensional spell - Complete Divine page 85
A transdimensional spell has full, normal effect upon incorporeal creatures, creatures on the Ethereal Plane or Plane of Shadow, and creatures within an extradimensional space in the spell’s area
- Incorporeal Target fighting - Ghostwalk, page 36
in meelee, everytime you miss because of a creatures incrporeal's miss chance, you can reroll your miss chance percentile roll one time to see if you actually hit
By the strategy of becoming yourself incorporeal why? - in the "rule compendium" (64) it is not mentioned that incorporeals have any miss chance of attacking other incorporeals.
Becoming incorporeal by a spell some examples are as follows:
- one with shadow - level 8 -Tome of Battle page 78
- ghost form - level 8 - Spell Compendium page 103
- Polymorph any object - level 8 - Player's handbook page 263
- greater wish - level 9 - Player's handbook
- umbral body - level 8 - Tome of Magic page 152
- any other way I may be missing...
By class feature:
- Shadow form - at level 3 of the Perfect Wight - Epic Level handbook pag. 34
- ghost strike - at level 8 of the Ninja - Complete Adventurer page 8
- spirit form - level 9 of the Spirit Shaman's - Complete Divine page 15
- any other way I may be missing...
Becoming a ghost Becoming Ethereal (Rule Compendium page 41) does not mean becoming incorporeal as only ghosts have the power to manifest (while being in the etheral plane they manifest as incorporeals in the material plane). This is also discussed in a previous question.
So if you make yourself becoming a ghost you could use the same strategy.
- ghostform spell from Spell Compendium (108) mentioned above
- any other way I may be missing...
By the strategy of making the incorporeal corporeal with a spell
- ghost trap - level 5 spell - Spell Compendium 103
- forced manifestation - ghostwalk page 52
- any other way I may be missing...
2 PART) When an incorporeal creature wants to attack an corporeal
By description of incorporeal subtype above (Rules compendium page 64) the following are ways to ignore the 50% miss chance:
Use a spell WHY? - Because spells have ha 50% miss chance if casted by a corporeal to attack an incorporeal, but incorporeal creatures casting a spell on corporeals have no miss chance. (not symmetric rule)
By Weapons
- attacks made with ghost touch weapons
- any other item I may be missing
Becoming corporeal by a casting a spell on yourself some examples are as follows:
- ghost trap - level 5 spell - spell compendium 103
- any other spell I may be missing
Becoming permanently corporeal this is discussed here
Limits of this answer: I tried to include as many information as I was able to collect and review but I am sure I have missed something, thus I will edit this answer if I recieve any comment or find new information.
Also, in regards to Pat Ludwig's answer, the rules of incorporeals where updated from the Monster manual 1. Some of the handbooks where you find the updated rules of the incorporeal subtype rules are as follows: Monster Manual III page 214 Rule compendium page 64 Tome of Battle page 79