Reddit reviews The Sublime Object of Ideology (The Essential Zizek)

I would say either The Sublime Object of Ideology or The Parallax View could be considered his seminal works and are widely regarded as legitimate works or critical thought by his peers. (Such as Ernesto Laclau, Michael Albert, Judith Butler, Chomsky, etc.)

People disagree with him, sure, but you should try reading his stuff. If you do, you'd realize that he has a really strange sense of humour, as is on display in this video. Zizek is not being serious about the flowers. He's merely providing a dissenting view of things, mostly to get viewers to think critically about things. You can't take this man at face value, you need to work a little harder than that.

As listed by Žižek in the film Žižek!:

• The Sublime Object of Ideology
  
• Tarrying with the Negative
  
• The Ticklish Subject
  
• The Parallax View
  
  Source

If you're looking for a good political read, this one.

If you want to get deep into the philosophy, this one.