I want a software advance than paint but less complicated than photoshop for creating diagrams for my scientific posters and publications. Kindly help.
Xara Designer Pro for vector graphics & websites (commercial and worth the price; 30 days free trial; very intuitive and easy to learn; using Xara is an enjoyable and incredibly effortless experience).
http://www.xara.com/
yEd Graph Editor for flowcharts (free; too good for no cost!).
https://www.yworks.com/products/yed
PyMOL for molecular graphics (version 0.99rc6 is free; too good...).
https://sourceforge.net/projects/pymol/
MarvinSketch for chemical schemes (free; too good...).
https://chemaxon.com/products/marvin
Python & MatPlotLib for plotting (free; too good...).
I like openoffice (or libreoffice) draw, both 100% free. There are tools for simple geometric shapes, but if you need to draw, say, a contour map, you can use the "points" tool set, which allows you to reshape your drawing to any desired form. At the end, you can export your drawings as PDF with 1200dpi, which is more than enough for most journals. You will need a different program to convert from PD to TIFF or JPEG later.
I agree with a reply previously posted. I use CorelDraw since many years and find this software extremely useful for figures (from very simple to more elaborated ones) and posters preparations. Basic commands are easy to understand and then you are free to explore the possibilities provided by this software.
I recommend Mind the Graph. It is an online platform to create scientific presentations, graphical abstracts or posters. There is thousands scientific illustrations available (www.mindthegraph.com).
Also, there is a blog with several tutorials to help the users (blog.mindthegraph.com)
I tried very interesting R, Statgraph, JMP, GeneStat, etc. There are several sofwares and each researcher should use one which is more appropriate for its purpouse.
I really like Grapher by Golden Software, which was not mentioned before. It is userfriendly tool for scientific data visualization. There are many types of graphics options, including rare species, for example ternary plots. The cost of the product is quite high, but there is Student License for 50$: https://www.goldensoftware.com/products/grapher
If you are used to work with R, package ggplot2 is top-rated and comes with serevera pre-defined styles, if you don't mind entering data manually inkscape is a great solution.
BioRender is awesome for first-timers and has a free version + student pricing. They have a library of scientifically accurate icons that makes it really easy to make figures fast. Here's a figure I made pretty easily in BioRender for a paper I wrote this year.