TITLE: Good software for linear/integer programming
QUESTION [17 upvotes]: I never did any linear/integer programming so I am wondering the following two things

What are some efficient free linear programming solvers? 
What are some efficient commercial linear programming solvers? 

It would be nice to supply a dummy usage example with each proposed answer.
Also what if wish to solve a integer programming problem? What are the answers to the above two questions in this case?
I know that integer LP is a hard problem but there are some relaxing methods that are sometimes employed in order to obtain a solution to an integer programming problem. Are there any software packages implementing this kind of stuff?

REPLY [2 votes]: I use lpsolve IDE, in addition to using lpsolve with R, with Python, etc.
Here is a list of some of the IDE features:

Everything is graphical and mouse controlled
Enter your lp model in all supported formats and even via an XLI
(external language interface)
Convert your lp model from any supported format to another supported
format and even via an XLI
Very user friendly editor to enter/change the model with syntax
highlight
Syntax checking of the model
Solve the model
See the results in grids
Control every possible lpsolve option (tolerances, presolve, scaling,
...)
View the matrix in grids
Export model to HTML, RTF, LaTeX output
Export matrix to CSV, HTML, RTF output
Export results to CSV, HTML, RTF output
Show statistics about the model.
...

More details: http://sourceforge.net/projects/lpsolve/