is there a web site to sell old ipads and itouchs?

Yes. eBay.

eBay Instant Sell http://instantsale.ebay.com/?search=ipad

Sell and Recycle Used Electronics - Gazelle http://www.gazelle.com/

For instant gratification in selling a used iPhone or iPad, Gazelle’s Gadget Trader, an iOS app, is tough to beat. In seconds it detects the device and reveals how much it is worth in good condition. Tap the Sell This Phone to Gazelle button and the deed is done.

Sell Electronics for Cash - Next Worth http://www.nextworth.com/

Buy My Tronics http://www.buymytronics.com/

Sell Your iPad http://www.sellyourmac.com/mac-product-guides/ipad.html

Totem http://www.hellototem.com/

How To Sell Your Old iPad: 5 Places To Trade In Your Old Device

http://www.huffingtonpost.com/2013/11/05/ipad-trade-in_n_4218964.html

THIS IS VERY IMPORTANT - What to do before selling or giving away your iPhone, iPad, or iPod touch

http://support.apple.com/kb/HT5661

Find My iPhone Activation Lock: Removing a device from a previous owner’s account

http://support.apple.com/kb/ts4515

Buying or Selling a Used iPhone or iPad Running iOS 7? Read This First!

http://www.makeuseof.com/tag/buying-or-selling-a-used-iphone-running-ios-7-read- this-first/

 Cheers, Tom 😉