It was my tower desktop that I first used one, making the SSD my C drive and the old HDD C drive becoming the D drive for data files.
The speed difference was really dramatic , far better than any cpu or memory upgrade etc.
It initially used this 60gb drive which still holds all my W 8.1 programs.
http://www.cclonline.com/product/17...GB-SATA-3-2-5-inch-Solid-State-Drive/SSD0206/
It also depends on what your existing cpu and mobo are as to how fast the SSD can run; an old Athlon or early Penitium might not allow the SSD to run at full speed. My old Pentium E5700/ mobo did restrict it, but still a gave that dramatic increase.
I recently bought a bigger 250gb one as well for another machine, equally as good.
http://www.cclonline.com/product/16...lid-State-Drive-SATA-6Gb/s-Internal-/SSD0125/
Both get good write ups, the 60gb one now half the price I paid , and the 250gb is still a decent price compared to the slower sata HDDs.
Do not get tied up with the masses of old web info about SSDs wearing out etc; the latest ones as said to be as long lived as HDDs; most of the big brands come with 3 or 5 years warranty.
The only thing to note is that you do not use Defrag on a SSD, it has its own TRIM instruction to clean it up, part of windows / supplied from the manufacturers software.