The Core i7 is the latest and fastest Intel CPU, although the above response is incorrect about the nature of the Core i7 architecture. Unlike the previous model Core 2 Quad, which was essentially two dual core CPUs on the same chip, the Core i7 is a native quad core architecture.
Core i7 features four physical cores with "hyper-threading", which allows each core to handle two threads simultaneously, resulting in 8 logical cores. It is actually more similar in design to the AMD Phenom CPU (also a native quad core design) than it is to Core 2 Quad. Like Core 2, Core i7 has individual L2 cache, but the size of this cache is much smaller than Core 2. Instead, Core i7 takes a similar approach to Phenom, featuring a large shared L3 cache.
Core i7 also features Intel QuickPath Interconnect (QPI), which replaces the FSB from Core 2. This is how the CPU interfaces with the motherboard, and its theoretical bandwidth is more than twice that of the fastest 1333MHz FSB available in the Core 2 line.
Core i7 requires an x58 chipset motherboard with socket LGA 1366 and will only accept DDR3 RAM. Apparently, Intel will produce no more Core 2 CPUs for socket LGA 775. The next desktop CPU release is rumored to be Core i5, which will utilize a P55 chipset and socket LGA 1156. Core i5 will be a cheaper, lower performance CPU intended for the mainstream market as Core i7 is currently targeted at the enthusiast or high-end market. Intel is also working on a 32nm process which will feature chips with more than 4 cores and chips that have the central processing cores on the same die as an integrated GPU.