Question: I was wondering how many official "*Republics*" there are in the *Star Wars* universe?

One, two, three? I know about the **Old Republic** and the **New Republic** but I was wondering if there are any more.

Can the answerer please use the Star Wars movies or *Thrawn trilogy* (I am reading the first book now) as reference because only some of my Star Wars knowledge is on the Expanded Universe.

Note: to limit confusion in answers please show your estimated time periods for each republic.

Answer: 
Generally speaking, DVK's separation into the New and Old Republic are correct. However, one could also argue that there were *three* Republics. Ruusan Reformations carried out after the New Sith Wars (Darth Bane era) ushered in a new "phase" to what we call the Old Republic. In fact, Palpatine refers to it in Attack of the Clones when he says "I will not let this Republic which as stood for a thousand years be split in two!" The EU has established that the Republic and Jedi Order are both around 25000 years old, but then why wouldn't Palpatine have just said that?
For comprehension, I rather see it as Wikipedia does. "The Old Republic" ~25000 BBY, that formed into the "Galactic Republic" in 1032 BBY, [19BBY-4ABY was the Empires rise] and then the "New Republic" as it was reorganised in 4BBY and then destroyed again in 34BBY in The Force Awakens.
So, two. But people often speak of the Old Republic and mean the "Galactic Republic" phase. At least as far as I understood!