I shoot a Canon 30D on land and a Sony F717 with Ikelite case under water.
You should buy a DSLR for the lenses as you upgrade the body.
Sounds like your G9 is right for you I shot my Sony F717 for a long time and have some great pictures. It is classified as SLR like you just can't change the lens. The K10 has great reviews as it has the weather seals. The Sony 100 is not bad either, but it all comes back to the glass you put in front of it. When I chose my camera I liked the Canon best for the lens choices.
I shoot a EFS 17-55 for everyday and a 100 macro for close up.
You know what they say though its not the camera that takes the great pictures, but the guy taking the shot.
PS I like that Nikon 12 MP hand held it looks like a nice point and shoot.