Intel Core i7 is New Quad Core processor which is going to replace i7 920 at same price point and offers better clock speed.

Intel Core i7 930 Processor Technical Specification:

Speed: 2.8GHz
Cache: 1 MB L2 and 8MB L3 Cache
Socket: LGA1366
Quad Core
Number of Threads: 8
TDP: 130 Watt
Intel Turbo Boost Technology
[...]

AMD Athlon II X2 255 – is one of the fastest (3.1 GHz) dual core CPU @ very affordable price.

AMD Athlon 2 X2 255 Technical Specification:

Speed: 3.1 GHz
L1 Cache: 128 KB
L2 Cache: 2 MB
Built on 45 nm Process
C2 Revision
Support for 32/64 bit
Socket: AM3
Supports DDR2/DDR3 RAM
HyperTransport 3.0
[...]

AMD Athlon II X3 440 – is one of the most affordable Triple Core Processor and offers more thread than dual core CPU @ cheap price.

AMD Athlon 2 X3 440 Technical Specification:

Speed: 3.0 GHz
L1 Cache: 128 kb
L2 Cache: 1.5 MB
32 / 64 bit
Built on 45 nm Technology
No L3 Cache
[...]

AMD Athlon II X4 635 – is one of the cheapest quad core processor and suited for Video works like 3D Rendering and Encoding @ cheap price.

AMD Athlon 2 X4 635 Technical Specification:

Speed: 2.9 GHz
L1 Cache: 128 kb
L2 Cache: 2 MB
No L3 Cache
Socket: AM3
Compatible with DDR2 and DDR3 RAM
[...]

AMD Phenom II X2 555 BE – Fastest Dual Core Processor form AMD for Gaming, Multimedia, HD Playback @ very affordable price.
Phenom 2 555 Black Edition Features unlocked multiplier for over-clocking.

AMD Phenom II X2 555 BE Technical Specification:

Speed: 3.2 GHz
L2 Cache: 1 MB
L3 Cache: 6MB
Socket: AM3
Support DDR2 and DDR3 [...]

Intel Pentium E5500 is affordable dual core processor for entry level desktop computers.

Intel Pentium E5500 Processor Technical Specs:

Code: Wolfdale
Speed: 2.7 GHz
Cache: 2MB
FSB: 800MHz
TDP: 65w
Built on 45 nm Technology

Intel Pentium E5500 Processor Price in India: Approx 4k Indian Rupee (INR)

Intel Core i7 980X is first Six Core Processor for Desktop computer with 3.33 GHz speed and built on latest 32nm Manufacturing technology.

Intel Core i7 980X 6 Core Processor Features and Specification:

Speed: 3,33 GHz
can increase up to 3. GHz with Turbo Boost
6 Core / 12 Threads
12 MB Cache
DDR3 Memory Support
[...]

Intel Core i5 661 – is similar to core i5 660 processor in Speed and specification but it offers higher GPU (Graphics) Clock Speed at same price.

Intel Core i5 661 Processor Technical Specification:

Codename: Clarkdale
Clock Speed: 3.33 GHz
Turbo Mode: 3.60 GHz
GPU Clock: 900MHz
FSB: 1333 MHz
Socket: LGA 1156
32nm Process
TDP: [...]

Intel Core i5 670 – High End dual core processor with speed up to 3.7 GHz (in Turbo mode) best for gaming and multimedia @ premium price.

Intel Core i5 670 Processor Technical Specification:

Codename: Clarkdale
Clock Speed: 3.46 GHz
Turbo Mode: 3.77 GHz
GPU Clock: 733MHz
FSB: 1333 MHz
Socket: LGA 1156
32nm Process
TDP: [...]

Intel Core i5 660 processor features dual core built on Nehalem Architecture with Integrated Graphics core.

Intel Core i5 660 Processor Technical Specification:

Codename: Clarkdale
Clock Speed: 3.33 GHz
Turbo Mode: 3.60 GHz
GPU Clock: 733MHz
Socket: LGA 1156
FSB: 1333 MHz
32nm Process
TDP: 73w
Dual Core
L1 Cache: 128kb
L2 Cache: 2×256kb
L3 Cache: [...]