No matter what your political orientation, Marx is essential. Don't believe what people say about Marx -- discover him for yourself.
Sociologists, economists, political movements of all stripes have been influenced by Marx. Even conservatives and right-wingers. (One reason the neo-cons have been so effective is that they count a number of ex-Trotskyites among their ranks.)
Marxism has been in decline since the 70s, but I suspect it will experience one of its periodic rebirths, as the effects of Peak Oil kick in (unemployment, depressions, wars for resources).
If you're interested in learning more about Marx, I'd start out with good general books from relatively neutral sources.
One classic is "To the Finland Station" by the literary critic Edmund Wilson. He has understandable explanations of Marxist ideas, plus a few chapters on the early anarchists, for those of you so inclined. Also some chapters on Trotsky and Lenin. It's hard to make sense of the 20th century without the background that Wilson provides.
I've found that small left wing parties are a bad place to learn about Marx. They tend to be dogmatic and (to my mind) intellectually dead.
Also, I'd avoid books that set out to "disprove" Marx; they're tendentious and have a superficial understanding of Marx. The best criticism of Marx come from the heavyweight philosophers and economists with a healthy respect for him.
A good source of current Marxist thinking is "Monthly Review," an independent and non-sectarian socialist journal. High quality and not too dogmatic. Einstein was an early subscriber.
http://www.monthlyreview.org/index.html
They just started a webzine:
http://www.monthlyreview.org/mrzine/ .