SSD - Solid State Drive. About a billion times faster than your old mechanical drive. Is this a regular PC or a laptop? You can add an SSD as your primary drive if you're doing a new install and just keep the other one for holding your media and other data files as a D: drive. In a laptop, you might have to swap it out and only use the SSD (but it will increase your battery life noticeably and still be tons faster).
I would suggest either of these:
Best value - good performance - less than power user -
Samsung 840 256GB
For best performance if you have SATA III connectors -
Samsung 840 Pro 256GB
For the first drive, what I mean by less than power user is that SSDs do wear out over time. The first one has a shorter life than the second (I won't go into specifics, just trust me). But if you're just doing web browsing and doing some office type stuff, it will last for a long long time (10+ years no problem). If you are pounding your harddrive with all kinds of media manipulation, database access etc, it may only go 3 to 5 years. Based on your response so far, the first will be fine for you. I don't over exercise my drive and the first would be fine for me, but I like high end stuff and went with the second.