Router with the best range?

Probably not. The combination of internal antennas and no aux connection easily available (though you can hack one if you really want) mean it's probably not your best option.

I've just spent some time working on this, and while my experiments have been largely with directional antennas, I'd have a look at D-Link's RangeMax line.

I don't know if the title is accurate or not, but the G ones seem to be very reasonably priced these days, the hardware looks ok, and they've got external antenna connectors so you can replace the stock one with something larger.

I'd guess that getting a semi-directional antenna and pointing it straight up would give you the best range in your situation, although depending on the stock antennae it might not be necessary.

Also, though I can understand the desire for G, doesn't 802.11a do better with walls and such? Since Apple's newer hardware supports A, it might be worth shopping around for an A router. Maybe somebody else has more experience in that department, though.

 

You could just drill a hole in your wet wall (wall with all the pipes that feeds directly to your basement), and feed a 50 foot ethernet cable into the basement.

Best place to access it would be a bathroom closet.

 

Linksys WRT-54GS with 3rd party firmware DD-WRT. Total cost ~$45.
The DD-WRT firmware lets you adjust the Xmit Power, though not recommend over 90 (default is 28) it can max out at 140? I currently have the Xmit Power on 38.