For the second half of the 1990s, my standard advice to people buying computers was to max out the RAM as the cheapest, best way to improve their computers' efficiency. The price/performance curve hit its stride around 1995, and after decades when a couple gigs of RAM would cost more than the server you were buying it for, you could max out all the RAM slots in any computer for a couple hundred bucks. Operating systems, though, were still being designed for RAM-starved computers, and when you dropped a gig or two of RAM in a machine, it screamed.
It's still good practice to max out your RAM, but it doesn't get you much of a dividend. The turbo-charger of the 2010s is solid-state disk-drives, and they're screaming up the same price/performance curve that RAM traversed twenty years ago. Two years ago, I traded my laptop drive for a 400GB SSD, spending as much on the drive as I had on the machine, and it was worth every penny. My laptop battery-life nearly doubled, and I stopped getting watch-cursors altogether; no matter what task I performed, it was done instantly.
In October, I bought a one terabyte SSD for a ridiculous $435 -- about a third of what I paid for a 600GB drive a little over a year ago! -- and having run it for two months now, I'm prepared to pronounce it good. I wasn't familiar with the manufacturer, Crucial, but they got very good reviews on Amazon, and at that price I was prepared to give them the benefit of the doubt. My machine -- a Thinkpad X230 running Ubuntu 13.10 -- chugs along with nary a beach-ball, and I can go six to eight hours on a six-cell battery with full brightness, and continuous Wifi and Bluetooth usage. I'm rough on my computer, and it's taken plenty of knocks and bumps without any noticeable impact on the drive.
To accompany the new drive, I bought a pair of $78 Toshiba USB3 1TB drives (one for backing up at the office, the other for my travel bag). They're nothing near as fast as the SSD, but combined with the USB3 bus, they're plenty quick for daily incremental backups, which take less than five minutes.
If your storage needs aren't as massy as mine, there's a whole line of Crucial SSDs, 480GB for $269, 240GB for $140 and so on. They all come with three year warranties, though I haven't had cause to get service for my drive yet (knock wood). The drive is 7mm high, and comes with an easy-to-fit adapter for 9mm enclosures.
I was less impressed with the adapter I bought to copy the files over; it was fiddly and prone to losing its connection. Ultimately, I slapped the new drive into a case in order to make the transfer.