First of all: I live in Germany, so I can only tell you prices in euros (they are mostly pretty much the same in US-$) and I can not support you with any links on where to get it. (expect if you want to order to Germany...)
Thanks for the inputs so far. I did not know about preamplification. I will need to look into that, as that may well be my problem.
As for how much I will be willing to spend - well, I'm not destitute. I'll spend what it takes. I don't need "The best of the best of the best - SIR". I just need something that works. I run the Digital Arts program at my local Boys & Girls Club. We will use this equipment for personal/learning projects, and for publicity videos for the club. I don't plan to donate this equipment, but to make it available for the kids as needed. I will also use it for my own projects. We need decent, rugged, and functional, but we're not professionals.
As has just been stated, I would also recommend the Zoom H4n, if you can afford it (about 300 euros). If you still have some money left, you can go for a shotgun mic, which could be Audio Technica or Rode, I have had good experiences with both. I would estimate this to be another 200 euros. So for 500 euros, you will get a very decent and flexible sound setup.
At a cheaper price, you can still get a shotgun mic to connect to your camcorder/computer. You should care about two things though: First, the mic has to have an option for battery power supply, since it needs power supply and the miniplugs won't support that. Second, be sure that you can return it wherever you buy, in case the preamps actually were your problem. You should also get a connecting cable. All pro mics have XLR outputs and you need an adapter to miniplug. Be aware that the length of the cable is very restricted (about 3 meters). If you want longer cables, you will have to go all XLR.
If you don't want to spend 200 euros on a shotgun mic, the cheaper versions of the external recorder (Zoom H1 for 90 euros, without external input; Zoom H2n for 180 euros with external input) are always a good idea to start with. They are also well suited to record any other audio from events, not just interviews, if you ever need this (concerts, performances, ...).
Finally, I want to mention: There are 3 types of mics that are interesting for you:
1. A shotgun mic. Very directional, only records sound from where you are pointing it. Good for interviews or camera work where the mic needs to be outside the screen (e.g. on a boompole above).
2. A lavalier mic. The little things you can clip on somebody's shirt. Useful for interviews and moderation, nothing else.
3. A condenser room mic. Those record all the sound in the room. Usable for interviews in silent surroundings and for room recording (concert etc...). The built-in mics of external recorders are of this kind.
Maybe that gives you a little more insight and you can start from here. I could write for pages about sound and mics and the "which one is the best"-war that this thread is about to start.
