Question: What is the latest version of iText? And what is the maven dependency for that?

Answer: 
You need to pay attention to the license for the Java version of iText:

* iText `2.1.7`: the latest **official** release by iText Group NV, under the `MPL` & `GPL` license, with `com.lowagie` groupId;
* iText `4.2.1`: the latest **unofficial** release by ymasory/InProTopia, under the `MPL` & `GPL` license, with `com.lowagie` groupId;
* iText `5.0.0` and higher: released by iText Group NV, under the `AGPL` license, with `com.itextpdf` groupId. One monolithic jar.
* iText `7.0.0` and higher: released by iText Group NV, under the `AGPL` license, with `com.itextpdf` groupId. Several modular jars.

Here you can find 2.1.7 and 4.2.x versions on Maven Repository:

Find before 5.x versions:
<http://search.maven.org/#search|gav|1|g%3A%22com.lowagie%22%20AND%20a%3A%22itext%22>

Find 5.x versions:
<http://search.maven.org/#search%7Cgav%7C1%7Cg%3A%22com.itextpdf%22%20AND%20a%3A%22itextpdf%22>

You may want to stick with the MPL & GPL versions, unless you are available to follow the AGPL license specification... 

EDIT: 
You should pay attention on which version you are choosing;

According to Bruno Lowagie comment, [versions 2.1.x are deprecated](http://lowagie.com/itext2) and should not be used due to technical and legal reasons.
iText 7 was released in May 2016. iText 7 is no longer one monolithic jar file, like iText 5 used to be. You use only those modules you need.

Put this in your POM file:

```
<dependencies>

  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>barcodes</artifactId>
    <version>7.0.0</version>
    <!-- barcodes depends on kernel -->
  </dependency>

  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>font-asian</artifactId>
    <version>7.0.0</version>
  </dependency>

  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>forms</artifactId>
    <version>7.0.0</version>
    <!-- forms depends on kernel and layout -->
  </dependency>

  <dependency>
      <groupId>com.itextpdf</groupId>
      <artifactId>hyph</artifactId>
      <version>7.0.0</version>
  </dependency>

  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>io</artifactId>
    <version>7.0.0</version>
  </dependency>

  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>kernel</artifactId>
    <version>7.0.0</version>
    <!-- kernel depends on io -->
  </dependency>

  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>layout</artifactId>
    <version>7.0.0</version>
    <!-- layout depends on kernel -->
  </dependency>

  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>pdfa</artifactId>
    <version>7.0.0</version>
    <!-- pdfa depends on kernel -->
  </dependency>

  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>sign</artifactId>
    <version>7.0.0</version>
    <!-- sign depends on kernel, layout and forms -->
  </dependency>

</dependencies>

```

This, and more information, can be found on <https://developers.itextpdf.com/itext-7-java>