Some good suggestions. Lots of choices. So it really is just a matter of preference.
If you want a pocket size camera (and you're OK without an optical viewfinder) I've only heard good things about the S90. My brother got one recently and says he hasn't used his Nikon D300 since.
The G11 is a bit larger, has an optical viewfinder and I'd guess better all around build quality.
Of the Canon P&S cameras, only those two have a bit larger sensor than the rest.
If a larger size isn't an issue, just weight, the SX20 (or something like the Fuji HC10) would give you a lot of versatility with their "superzoom" lenses.
The 4/3 format cameras look nice and have larger sensors than the point and shoot cameras. And again, if you can be satisfied without an optical viewfinder, those without prisms are very small for a camera with an interchangeable lens - but so far the choices of lenses is pretty limited unless you mount a full size lens on one which would seem to defeat the purpose if you are trying to get a lot smaller and lighter.
If you have the Iphone 4, doesn't it have a 5MP camera? That should be good enough (I don't know anything about the lens) for casual snapshots and it's with you all the time, so maybe that's enough for when you are not planning on needing a more "serious" camera.
I used to have a Canon S400 (got stolen). The 4MP on a tiny sensor still got great results when I used it to travel and didn't want to carry a big camera with me, but wanted to have a camera all the time (I bought it to take with me on a trip to parts of Asia I had never seen before.. I wore it on a belt case, but now they make much slimmer camera that can be more easily carried even in a small pocket. I replaced the S400 with an SD450 - it's a good deal smaller than the S400 was, but still big compared to what's available from companies like Casio and a bunch of others.
Leica makes a little point and shoot camera that I've heard is great, but I've never used one and don't know anyone who has one. But I was told by the guys that own the local camera store that it's a superb camera....they carry several brands of P&S cameras and only Nikon SLRs...The owners are 3 old pros and they seem very knowledgeable about their products. They don't carry Canon for whatever reason - so I don't know how the Leica compares to the G11...seems like a pretty similar type camera. Also about the same price.
Right now I own cameras in all sizes from larger than the 7D down to the old SD450. The camera I seem to get the most use out of for personal use is my SX10 ...it's not particularly small, but it is very light and I like the versatility of the 20x zoom. And the image quality is actually very good considering the small sensor and the extreme range off the zoom (the IS works very well and is very very quiet).
Best of luck,