Well, one piece of open source software I'll certainly be using is Audacity, for editing audio files. It's as good as anything around for simple podcast editing. GIMP is *not bad* for photo editing although I'm much more familiar with Photoshop (and more qualified to use it).
I'd not consider GIMP "fit-for-purpose" for heavy/major image work. I use it (because I work on Linux) and it is a pain in the... compared to Photoshop.
When it comes to design for brochures and booklets (for example) I'd use Adobe Fireworks to create any graphics or images I'd need.
Have you tried Inkscape (FOSS vector image editor)? I used to use Fireworks a lot and Inkscape turned out to be, surprisingly, a worthy upgrade on that. But there can be a learning curve if you're only a casual Fireworks user. Worth considering.
Hopefully the above answers Tom M's question too. Beyond those pieces of software I can't imagine I'd use the rest of Adobe CS at the moment - although Dreamweaver may be useful for designing emails to members and donors.
Oh noes! Please don't :P
Maybe try something like MailChimp's campaign editor (literally the best mail design tool ever!). Dreamweaver sucks bad enough for creating websites, let alone email ;) In fact - it might be worth looking at MailChimp for the Chapters mail campaigns/correspondence.
On the main topic: I have a few CS Licenses kicking around which may include some of the software you need (no promises, I just know they exist somewhere, not the state of them :P). Let me have a look.
Tom