I’m looking a good tool for drawing figures and diagrams for thesis and research papers.
According to my findings, it seems like inkscape is a good tool for that purpose. Do you have some better ideas?
It depends on what sort of diagrams you need, but Dia makes it easy to create various types of flowcharts, graphs, maps, etc.; is available for Windows, Mac, and Linux; and is free.

If you have Microsoft Office, then Visio is the perennial tool for this task.

I think you can use Dia Diagram Editor it is a free software and you can download it from the link below.
Within academia Latex is a very popular authoring tool for documents. A stackexchange site for Latex users is Tex - Stackexchange.
Within Latex a popular tool for making figures is Tikz. A site showing a wide range of Tikz figure is http://www.texample.net/tikz/examples/.
One of the examples from the site is shown below: (Source: http://www.texample.net/tikz/examples/parameterized-plots/)
