GL_RGBA with GL_UNSIGNED_BYTE will work. It means 8 bits per component, where the components are in order red, followed by green, followed by blue, followed by alpha (opacity).
AFAIK: GL_RGBA with GL_UNSIGNED_INT_8_8_8_8 may work. It means that there is a 32 bit word packed with 8 bits each for red, followed by green, followed by blue, followed by alpha. However, the problem is the endianess of the platform in use. It will work if your platform uses big endianess. If, on the other hand, your platform uses little endianess then you have to use GL_RGBA with GL_UNSIGNED_INT_8_8_8_8_REV instead. (May be I'm mixed up little and big endianess here; maybe its the other way around).
Edited by haegarr, 06 August 2013 - 12:45 AM.