Few will dispute that the very best bang for your buck today is the Solid State Drive. Quantum leaps forward in speed, and reliability over the mechanical HDD.
Until now, they've been rather pricy. However, the price drops in just the past few months have been staggering!
Here's an outstanding SSD, spec'd at 240GB, with both read & write speeds in excess of 500 mb/s on a SATA III port, for only $139.00. A year ago, a drive like this would have cost about $350.00
Similar drives are available these days with 120/128GB capacities for $60.00~$70.00
I can tell you from my own personal experience they make incredible laptop upgrades. A laptop that normally takes 1 minute & 20 seconds to fully boot up, will take about 16 seconds with an SSD. Applications will open in a fraction of a second, and games will load in 1/5 the time it takes on a spinner.
I thought I'd post this sale, if anyone is interested...
Newegg.com - Corsair Force Series 3 CSSD-F240GB3A-BK 2.5" 240GB SATA III Internal Solid State Drive (SSD)
HAF 932 Advanced / Corsair AX1200 / Asus Rampage IV Extreme / i7-3930K / H100 Cooling 4x120mm
16GB Corsair DDR3 / GTX 580x2 SLI + GTX 460 PhysX / SSDs Mushkin 240GB, Crucial 256GB, Crucial 512GB