The SSD is the fancy toy for the PC, because the price is going up now and you hard to find the best deal like a couple of months ago. If you have the budget to buy one, as long as you start use the SSD then you ever go back to use the HDD again, even it only boot the PC, open the programs, and load the games fast something like that.
Now newegg.com has the sale "SAMSUNG 840 Series MZ-7TD120BW" for $90 with promo. code: EMCXVXW59. If you have other regular HDD you need at least the 120GB SSD for the OS, programs, and some games.
It is high-end entry-level SSD, you can find some review online. If your case don't come with 2.5 Inch HDD/SSD Mounting Kit then you need get one too.
HDD/SSD Mounting Kit: http://www.newegg.com/Product/Product.aspx?Item=N82E16817994139