I'll have a go...
I2C (=IIC =Inter-Integrated-Circuit)
Intended for communication between IC's on a single board but sometimes used between boards.
Only two signal wires needed: clock and data
Single duplex
Not usually fast - 100Kb/s and 400kb/s are the usual modes. Faster are available but not widely supported.
IC's each have a selectable address, allowing selective communication with multiple devices on the bus
True multimaster - with collision avoidance and bus arbitration
I2C-Bus: What's that?
SPI (Serial Peripheral Interface)
Three or more signal wires needed (clock, data in, data out and multiple slave selects)
Full duplex operation
Fast - typical rates of 10MHz, 20MHz or much faster especially on FPGA
With multiple devices on the bus, the target must be selected by an out-of-band chip (slave) select wire
Devices operate as master, slave or both
Serial Peripheral Interface Bus - Wikipedia, the free encyclopedia
RS-232
One or more signal wires (TX, RX, ready to send, clear to send; simplest one-way might just use one wire - TX or RX)
Generally intended for communications between just two devices
Handshaking wires can be optionally used for control of data flow
Typically used for long, inter-equipment links
Asynchronous, needs accurate data rate control and oversampling at the receive end for high speeds
Typically slow speeds (from 300 baud to 115,200 baud) but much faster is possible on very fast custom logic
True RS232 typically uses around +/- 12V for RX/TX levels - needs a level converter to logic but gives long possible cable length
Logic-level RS232 (e.g from an MCU) is more susceptible to interference over long distances
RS-232 - Wikipedia, the free encyclopedia
Does that give you a starting point?