To decrypt these for the BitcoinQT wallet is to visit www.bitaddress.org and go to the tab wallet details and paste your private key on the paper wallet into the wallet details field and click view details.
True that! However you should never post your private key onto a live website. I strongly recommend you instead download the GitHub ZIP file of bitaddress.org / bit2factor.org / bitcoinpaperwallet.com and run the HTML file from your local computer, in case the live website has been compromised. (Happens to bitcointalk.org all the time, figure it will happen to one or all of the other services at some point.)
Also a plug for bitcoinpaperwallet.com: the "validate" tab (like the "details" tab on bitaddress.org) has a QR code scanner so you can use your webcam instead of having to type in the whole private key.
Relevant:
https://bitcoinpaperwallet.com/bip38-password-encrypted-wallets/
https://bitcoinpaperwallet.com/how-to-scan-qr-codes-with-camera/