I currently work on two great programs- GIMP for raster graphic, and Inscape for vectors. Without GIMP and it's plug-ins I would be long gone :). For example I found ease way to slice images - really helpful script as I'm producing paintings (digital paintings - printing on canvas) and I need to slice 500 images in the same way for 5 part paintings. You just make empty layers with names you want the image to have for example slice-one.jpg and after installing this script you just click "layers slices" and you have ready images :) in this case one.jpg.
If any of you have any questions about this programs - ask, If I will be able, I will help :)
And what do you use except of Photoshop and Corel?