I would like to give my testimony on GIMP and Quanta+. They have been used by Quantum Computer Solutions cc, an SME, as the only web development tools and they are fantastic. I don't foresee our company ever purchasing any proprietary software except for Macromedia Flash or is it Adobe Flash nowadays. Open Source software has really covered this area for me.
Quanta+ allows me to easily edit and manage file uploads well. It also has accomodates various plugins such as sysntax checkers, diff, spellcheckers, image mapper etc. It's highly configurable. The WYSIWYG editor is still not up to scratch though, but I rarely use that. I like being in full control of my html code.
GIMP is a Photoshop equivalent. I use it to produce graphics and edit images. I have become so comfortable with it that I don't think I will ever move away from it. Its short fall is color management when it comes to printing for the press. But in the realm of web design, of which the websites will be viewed only on monitors, its works well.
These two great tools are complimented by PHP, another great open source product. I use PHP to add functionality to a website and PHP does a great job at that.
You can view our portfolio here
http://www.quantum.com.na/portforlio.html. All except the Healthcare Medicals and Pharmaceuticals & Zila Designs websites have been created using OSS.
Well that's my testimony. Would like to here what the rest of you think about the software mentioned above.