Canon G 15

As a point and shoot, it doesn't get a lot better than the G15. I don't see it being much better than any other P&S for shooting coins, though, because it'll have the same limitations. Any lenses and adapters for it will be add-ons; the original lens is not removable. The G15 is intended for the photographic power-user who wants full manual control over the imaging process.

If you're just looking to shoot coins, and want to spend that kind of money, rmpsrpms' idea is by far the better way.

You cant change lenses on a G15 , its definitely better than an average compact camera in terms of image quality but its not as good as an SLR. If you want better quality pictures from a compact camera change the image quality settings to a resolution that is 50-60% of the headline resolution- this will result in more detailed images ( with less noise) , that have smaller file sizes for uploading onto the web .

Yes, a 50 with a 2x converter will perform similarly to a 100mm and yes, the 90mm lenses are pretty darn good in their own right. I think the 50/2x might be particularly rewarding, for cheap. If the 50 does not have its' own aperture ring, be sure the converter can share electronic signals with the camera. Some do not.

OK, now that I'm off work for a bit (I work crazy hours), I've had the chance to do some research on your behalf and the news isn't good. Not for your wallet, anyway.

Canon's Life Size Converter - turns your 50mm into a 100mm, all camera functions intact - will cost more than the lens itself. That puts you into 100mm territory. Kenko, a reputable aftermarket producer, offers a set of 3 extension tubes which will pass the camera's electronic signals, but those are pricey too at ~$200. You can buy cheap, non-electronic extension tubes, the tradeoff there being the only way you can set an aperture is to hold the shutter button down halfway (with the lens only attached), remove the lens and attach the extension tube(s) while still holding the shutter button down, and then reattach the lens/tube combination and take the shot.

Near as I can tell, that will require three hands. If you're so equipped, you're good.

This may be a time to also consider the bellows/duplicating lens setup we're so high on here. Some fabrication of mounts might be necessary, but the total cost of such a setup including a decent lens will be quite a bit less than even the 50mm Canon Macro.

The Tamron 90's I see offered on ebay (Canon-specific) for <$300 are the previous generation units, and are relative bargains since they're a generation old. The advantages of the newer Di lenses - better coatings and Image Stabilization - aren't really relevant to coin imaging. I think you'd be pretty happy with such a lens.