IF- I repeat IF- you determine that the issue is not on the internet end, but it is your router- (you can try by connecting a computer right to the modem for a bit)-
A POSSIBLE issue is interference. We had HORRIBLE ping times over wifi in my apartment because everyone was running 2.4 Ghz wifi routers, and there were so many they ran out of channels. A way to get around this is (if some/all of your computers support it..) is going to a dual band wireless N router. Dual band runs on 5 Ghz as well as 2.4 Ghz, and the 5 Ghz band has more channels, and doesnt go QUITE as far (but usually fine for inside a residence) so you have less interference from 500 feet away, more channels available to spread out the load (decent modern routers automatically choose open channels) and also less people use it.
Note- not all wifi cards support 5 Ghz. You can still run 2.4 Ghz, but of course you loose this benefit.
You can see this by using a program that can show you wifi traffic, such as the free inSSIDER. See if there are overlapping channels- or even if you can set your router to a better free channel range.
http://www.metageek.net/products/inssider/ (When we run it here, there are at least 2 networks on every 2.4 Ghz channel, and half the spectrum has 3 per channel.... not ideal) (5 Ghz only has 3 networks, and they are spread out.)
Also, older routers can slow down when serving too many computers. We noticed a huge speed boost even on the 2.4 Ghz spectrum when switching from our (basic and 2.4 Ghz only Wireless N belkin router) to a nice dual core dual band Asus router. It simply was able to keep up better. Note, I am in a large shared apartment, and often 5 or more people are using the internet at once for various reasons.. add in wifi on phones etc and it got quite bad.
However, we are happy with our (expensive and non-mustachian, but for us very worth it) Asus RT-N65U. (Its processor is dual core! Thats just cool, and it does NOT slow down.) - Early versions overheated, but they have updated the firmware. It runs great now, and asus has a good warranty.
Lastly, check out inSSIDer first- it is very likely you live in an area with less people and have lower demands all around. (Dual band is nice- but you really dont need it if 2.4 Ghz is clear.)