Mini DV is a good choice, however High Definition is becoming almost a standard soon and prices are going down very fast. If You had a chance to see some of my videos on YouTube, they were shot with High Definition camera. You can't appreciate picture quality there because it had to be down converted to low resolution anyway but You will appreciate it on Your computer screen or plasma if You already have one. Mini DV (and DVD) frame size is 720x480 (NTSC) but HD frame size is 1440x1080 or 1920x1080. That's huge difference from already good looking DV, so take that into consideration, especially when You think You don't buy new camera that often. High Def is also nice because it records in wide screen which is beautifull and has this cinematic look.
Now for what You don't want is the camera that records on DVD disc for simple reason that this is MPEG-2 format which is not so good when it comes to editing, so don't buy it. It has to record either on miniDV tape or hard drive. Many of new cameras offer hard drive recording and this is also good because saves You time when You capture footage to Your computer (with tape it is real time, means 1 hour of footage takes 1 hour of capture)
When people buy camera, sellers often say "this one is great because it has 700x zoom". Forget about it, this is digital zoom and it's not good at all, actually, the first thing You do is go to the menu and turn it off. You are only interrested in optical zoom. Also a good thing is "Optical image stabilisation". You also want good low light capabilities (which is actually unreal, You need good light for good image no matter what)
To connect Your camera to computer You use "Fire wire", a cable You buy separately, today every digital camera has this connection. When it comes to brand in video, the good ones are Sony, Panasonic, Canon. Lens is the heart (or eye I should say) of the camera. If You decide to buy Sony, get one with Carl-Zeiss lens. If Panasonic - buy one with LEICA lens. Canon uses Canon (also great) lenses. No Samsung or JVC (at least not in the consumer market, they make nice Pro equipment though)
As a freediver You also want Your camera to be possibly small so it will fit in a small housing, but today that is not an issue anymore (actually some things got even too small)
I forgot to mention that to edit High Definition video You will need very, VERY powerfull computer and Apple Macintosh is always recommended as this machine is simply made for it. Video editing in general is quite demanding task, PC's are OK, it's Windows that can't handle it very well.
Let me know when You find camera You like
Peter