The motherboard usually has 2 chipsets
1. Northbridge - for Intel LGA 775, it holds the Memory Controller and the PCI-E Controller. The Northbridge determines the type, maximum amount, and maximum speed of memory. It also determines the number of PCI-E lanes that will be available.
2. Southbridge - it handles the Input/Output devices (keyboard, mouse, gamepads), storage devices (HDD, SSD, USB) and other components of the PC
Modern AMD and Intel CPU's now have an Integrated Memory Controller. So it is now the CPU that determines the type, maximum amount, and maximum speed of memory. The Northbridge is now only left with the function of supplying the PCI-E lanes. Modern CPU's don't use the FSB anymore, they now communicate directly with the memory
For Intel LGA 1156 motherboards, there is only one main chip - the Platform Controller Hub. It functions more like a Southbridge and the 2 common chipsets are P55 and H55. The main difference between P55 and H55 is that H55 allows the use of IGP's of Intel Core i3 500 and Core i5 600. Using a Core i3 500 or Core i5 600 on a P55 board is possible but the IGP will be disabled. All LGA 1156 processors are compatible with P55 and H55.
Intel LGA 1366 boards still has two chips- the Northbridge and the Southbridge. It only has one type of Northbridge - the X58. The X58 chipset has 36 PCI-E lanes but this becomes only significant in a multi-GPU setup.
Here are the common Intel Northbridge chipsets for LGA 775
(Chipset - maximum FSB supported - memory type - maximum memory amount - PCI-E Lanes)
P31 - 800/1066 MHz - DDR2 667/800 - 4GB - 1 PCI-Express x16 / 1 PCI-Express x4
P35 - 800/1066/1333 MHz - DDR2 667/800/1066 - 8GB - 1 PCI-Express x16 / 1 PCI-Express x4
P35 - 800/1066/1333 MHz - DDR3 800/1066/1333 - 8GB - 1 PCI-Express x16 / 1 PCI-Express x4
G31 - 800/1066/1333 MHz - DDR2 667/800 - 4GB - 1 PCI-Express x16 / 1 PCI-Express x16
P45 - 800/1066/1333 MHz - DDR2 667/800/1066 - 16GB - 1 PCI-Express x16 2.0 / 2 PCI-Express x8 2.0
P45 - 800/1066/1333 MHz - DDR3 800/1066/1333 - 8GB - 1 PCI-Express x16 2.0 / 2 PCI-Express x8 2.0
X38 - 800/1066/1333 MHz - DDR3 800/1066/1333 - 8GB - 2 PCI-Express x8 2.0
X38 - 800/1066/1333 MHz - DDR2 667/800/1066 - 8GB - 2 PCI-Express x8 2.0
X48 - 1066/1333/1600 MHz - DDR3 1066/1333/1600 - 8GB - 2 PCI-Express x8 2.0
X48 - 1066/1333/1600 MHz - DDR2 667/800/1066 - 8GB - 2 PCI-Express x8 2.0
Here are the common AMD Northbridge chipsets
(Chipset - PCI-E Lanes - IGP - supported Southbridge)
890FX - 2 PCI-Express x16 2.0 / 4 PCI-Express x8 2.0 - none - SB850/SB810/SB750/SB710
890GX - 1 PCI-Express x16 2.0 / 2 PCI-Express x8 2.0 - HD 4290 - SB850/SB810/SB750/SB710
790FX - 2 PCI-Express x16 2.0 / 4 PCI-Express x8 2.0 - none - SB850/SB750/SB600
790GX - 1 PCI-Express x16 2.0 / 2 PCI-Express x8 2.0 - HD 3300 - SB750
785G - 1 PCI-Express x16 2.0 - HD 4200 - SB850/SB810/SB750/SB710
Here are the common AMD Southbridge chipsets
(Chipset - sATA ports - USB 2.0 ports)
SB850 - 6 x 6GB/s - 14
SB810 - 6 x 3GB/s - 14
SB750 - 6 x 3GB/s - 12
SB710 - 6 x 3GB/s - 12
SB600 - 4 x 3GB/s - 10