Optimizing wireless router speed and minimizing interference

About which channel to use, the book "Wireless network coexistence" by Robert Morrow has this to say:

In north America, a non-overlapping set consisting of channels 1,6, and 11 or an overlapping set composed of channels 1, 3 5. 7, 9, and 11, can be selected. The corresponding sets in Europe are channels 1, 3, 5, 7, 9, and 11, can be selected.

To detect interference, you might use a WiFi finder to map out your environment.
This article discusses several such utilities.

If it's just you using it, then there's a decidedly low-tech solution in the form of a tin can! Go have some beans, clean the can, poke a hole in the bottom, and put it over an antenna (if there are two antennas, then that's even better, other people won't lose out!), then point it at your PC. It'll focus the signals, hopefully drowning out any other local routers.

as far as finding a clear channel, you can use wifi analyzer which is a free app for android powered smart phones with wifi. it's an easy to use app that shows all networks in range, what channel they are on and rates the channels from best to worst according to how much traffic/interference is on that channel. granted it's not a rf spectrum analyzer scanning for interference from other, non-wifi sources such as microwaves and telephones/cellphones; however it works for low level tweaks. they may have something similar for the iphone or other phones but definitely something to look into if you have a smartphone with wifi built in and still having this issue after over a year ;-P just love to bump. and the bean can works, i have been trying to style and fabricate a cone shaped directional antenna so it would cover a wider area but so far haven't found a solution.

If you are running a Unix of some kind, try

sudo iwlist wlan0 scan | grep Channel

http://en.wikipedia.org/wiki/Wireless_tools_for_Linux#iwlist

iwlist is used to scan for available wireless networks and display additional information about them that is not displayed by iwconfig. The main argument is used to select a category of information, iwlist displays in detailed form all information related to this category, including information already shown by iwconfig. The command is primarily used to generate a list of nearby wireless access points and their MAC addresses and SSIDs.