IWRAM: Internal (on the same chip as the CPU) work ram. 32kb large on a 32 bit bus. Generally holds the most critical data (ARM code, time sensitive data, etc).
EWRAM: External (not on the same chip as the cpu) work ram. 256kb large on a 16 bit bus. Slower than the IWRAM. Holds anything that'd go in WRAM that isn't stored in the IWRAM. Can hold code, but since it's on a 16 bit bus it has to be ARM THUMB code.
BIOS: The BIOS, don't touch this.
PALRAM: Palette ram. 1KB Want to swap the colors? Have fun.
VRAM: Video ram. 96KB. Holds the actual data drawn to the screen.
OAM: Object Attribute Memory. 1KB. Contains the actual "object" of things such as sprites (the mode, the size, what palette to use, etc).
ROM: The ROM file.
SRAM: Saveram. Want to corrupt a save file? Corrupt this.
Combined WRAM: IWRAM and EXRAM combined into a single memory domain that contains both.
System Bus: Theoretically allows access to everything that's mapped as it facillitates the communication between pieces of hardware. In execution, not everything mapped will be visible through this domain. It's a matter of if it was properly exposed or not. Corrupt something here and it'll be reflected in the domains derived from it.
0x00000000 - 0x00003FFF- 16 KB System ROM (executable, but not readable)
0x02000000 - 0x02030000- 256 KB EWRAM (general purpose RAM external to the CPU)
0x03000000 - 0x03007FFF- 32 KB IWRAM (general purpose RAM internal to the CPU)
0x04000000 - 0x040003FF- I/O Registers
0x05000000 - 0x050003FF- 1 KB Colour Palette RAM
0x06000000 - 0x06017FFF- 96 KB VRAM (Video RAM)
0x07000000 - 0x070003FF- 1 KB OAM RAM
0x08000000 - 0x????????- Game Pak ROM (0 to 32 MB)
0x0E000000 - 0x????????- Game Pak RAM