The cartridge design is not very space- efficient so for the Pentium 4 and Core CPUs Intel reverted to a socket approach. The initial socket designs used a slightly modified type called Flip Chip PGA (FC-PGA). This reverses the orientation of the CPU die to male better contact with the heatsink. The FC-PGA2 also added a heat spreader to the package.
The next socket type used by Intel, Land Grid Array (LGA), saw the pins move from the CPU to the chance of damaging the motherboard. AMD have used this form factor once (for Socket F) but usually persist with PGA-type sockets.
The following tables summarise some of the various socket types that have been used over the years. Note that the supported desktop processors and memory are illustrative rather than definitive. For more up-to-date information, visit a site such as CPU World, Tom's Hardware or X-bit Labs.