Your router may not be giving your iPod a valid IP address. Go to Settings > Wifi > your network name and touch the ">" to the right to see the network details. If the IP address starts with 169 or is blank then your router didn't provide an IP address and you won't be able to access the Internet. The 169.254.x.y is a link-local address and is intended only for communication on the local network. The x and y are random numbers. The iPad assigns this address when it receives no IP address from the DHCP server (which is probably your router). This allows communication on a local network with no DHCP server. This is sometimes referred to as an "ad-hoc" network.
Your other devices may continue to function with their existing IP address even if the DHCP daemon in your router is no longer issuing address. The fact that other devices on the network continue to work should not lead to the conclusion that your network router is faultless.
Sometimes the fix can be as simple as restarting your router (remove power to the router for 30 seconds and then restart). This works because the DHCP daemon in your router will be restarted upon a router restart. Next, reset network settings on your iPad (Settings > General > Reset > Reset network settings) and then attempt to connect. In other cases it might be necessary to update the router's firmware with the latest from the manufacturer's support web pages.
If you need more help please give more details on your network, i.e., your router make, model and version, the wifi security being used (WEP, WPA, WPA2), etc.