If you are a student you can buy Lightroom in the student store for $99. Spending all the time learning how to use a “free” program and then later switching to something else is a real waste of your time, since the learning curve is about the same, no matter which program you use. Better to spend the time learning one program and spend the rest of it being creative.
There is a reason the superior, commercial products are purchased by those interested in doing post production on their images. Quality and flexibility are two that stand out as important features of any product used in photography.
If free programs were that good, Adobe, Corel and others would have go out of business long ago.

The Gimp is free and has a lot of the Photoshop features.http://www.gimp.org
If you like the photoshop look you can use gimpshop – based on Gimp it has Photoshop look and feel and many Photoshop tutorials can be used for creating effects. Does not support Photoshop plugins.http://www.gimpshop.com/

follow these linkshttp://www.picnik.com/http://www.gimp.org/