Well I just love The Clash to death, but I have to be honest: there is absolutely no reason for The Singles to exist. It's a compilation, and an honest one (in that it is exactly what it purports to be: a collection of the A-sides of Clash singles and nothing more, nothing less), but a meaningless one.
Because, quite simply, the WORST way to get acquainted with The Clash is through their singles. This is not to say that their singles were bad (though some, like "Remote Control" and "Hitsville U.K." are pretty darn weak); in fact, some of their most memorable songs, like "White Riot," "(White Man) In Hammersmith Palais," "London Calling," and "Train In Vain" were singles. But SO much of their best work is NOT here, simply because it didn't make it out on the topside of a 45. To the extent that a large preponderance of their finest music didn't come out on singles The Clash were an ALBUM act, unlike say the early Who. So what this CD gives you is a wholly unsatisfying and incomplete view of the greatness of this band.
As an alternative I'd recommend one of two options: if you (like me) dislike compilations as a rule, go buy their debut and London Calling, both of which are considered absolute classics, and if you like what you see, explore further. If you're a casual fan, go get The Story Of The Clash, which in its remastered form shouldn't be that much more expensive than this disc; it's also a bit incomplete (and sequenced oddly) but it provides a much more well-rounded view of The Clash.