Becoming a ghost.

[Ichneumon]

Is there any in game way for your character to become a ghost?

[Maryring]

Die with unfinished business.

As I understand, there is no hard and fast rules to make you a ghost. You can only hope that you return once you have died, so that will be up to the DM. He can decide wether or not you become a ghost after you've died.

[MinusInnocence]

Given the ghost's level adjustment it's likely the DM will require you to take the template in levels, a la Savage Species. As for the reasons you might take the template in the first place... it's difficult to adjudicate the difference between someone dying during the course of adventure and dying before completing their quest.

Whatever is tying you to the mortal realm should be sufficiently epic or you would have gladly gone on to the afterlife (unless you're evil and aren't looking forward to an eternity in the Lower Planes). It's not like the guy who falls off a rope and breaks his neck while robbing some tomb will come back as a ghost until the treasure he was searching for is claimed. Then again, in lots of ghost stories all it takes is for someone's body to be left out to rot in the sun; they just want a proper burial.

[dauphinous]

Declare your interest in such a concept to the DM privately. Same with trying to use the Risen Martyr PrC. If the DM thinks it's okay and is willing to deal with it, work with him/her to contrive a circumstance that will make it happen. Expect to be the one doing most of the work, but the DM's input would really be required to make sure it fits with the story.

[Fax Celestis]

Take levels in the Psion Uncarnate PrC.

[Shiny, Bearer of the Pokystick]

Alternatively, there's Ghostwalk, but dang if that isn't the biggest hornswaggle of alternate rules and setting-specific stuff-and-nonsense I've ever seen.

Nice 'ghost classes' and very nice 'ghost feats', though.
And a lot about becoming a specific kind of ghost.