I have little to no signal stregth from my router. You literally have to stand right next to it to get signal. I, unfortunately, assumed it was the router so I bought a new one and set it all up- same problem. I live in a small house and am never farther than 20-30 feet of the router. Internet connection through Ethernet seems to be strong and fast... My wife and I have 2 apple computers, iphone, blackberry, appleTV, and playstation 3 ALL having problems with it.
It may just be plain ol' interference issues. One of the problems w/ wireless is that the 2.4GHz freq is not reserved for wireless routers. It's an "open" freq available to just about anyone/anything who wants to use it. That includes microwave ovens, cordless phones, baby monitors, wireless keyboards/mice, etc., and of course, other wireless routers. The fact it didn’t change when you replaced the router further suggests it’s interference.
Did you try placing the router in another location (preferable centrally located), and/or elevated by a few feet?
Do you have any unusual environmental conditions? I once lived in an house w/ plastered walls that were so old and hard, they had been virtually petrified! Trying to get wireless signals around the house was like dealing w/ lead walls!
Its in the most centralized location it could be, off the ground. Another thing worth mentioning is that its worked fine for a year and we have only had problems last few weeks. Went out and bought a new router this week and same thing...