Actually just got ours working again. I followed the advice of JimHdk in the following link: https://discussions.apple.com/thread/3869371?start=0&tstart=0
Hopefully it helps you out too!
Edit: something I forgot to mention was to check the ip address that your wireless network is giving your iPad. If it is blank or begins with 169then apparntly your router has given it a faulty IP address which would indicate while it says you have full signal strength yet no internt connection.
Look at iOS Troubleshooting Wi-Fi networks and connections http://support.apple.com/kb/TS1398
iPad: Issues connecting to Wi-Fi networks http://support.apple.com/kb/ts3304
iOS: Recommended settings for Wi-Fi routers and access points http://support.apple.com/kb/HT4199
Additional things to try.
Try this first. Turn Off your iPad. Then turn Off (disconnect power cord) the wireless router & then back On. Now boot your iPad. Hopefully it will see the WiFi.
Change the channel on your wireless router. Instructions at http://macintoshhowto.com/advanced/how-to-get-a-good-range-on-your-wireless-netw ork.html
Another thing to try - Go into your router security settings and change from WEP to WPA with AES.
How to Quickly Fix iPad 3 Wi-Fi Reception Problems
If none of the above suggestions work, look at this link.
iPad Wi-Fi Problems: Comprehensive List of Fixes
Fix iPad Wifi Connection and Signal Issues http://www.youtube.com/watch?v=uwWtIG5jUxE
1. Have you tried rebooting router?
2. Reset network settings
3. Have you tried changing the security settings e.g. WEP, WPA, WPA2
4. Have you tried changing channel; try channel 1, 6 or 11 (non-overlapping channels)?
5. Reduce the number of walls between your iPad and the router.
6. Have you tried changing wireless protocol e.g. a/b/g/n