I've used Visa gift cards to pay all sorts of things online for about three years now. The only place it's not worked is OGPlanet because they require "Verified by Visa" which is a program that giftcards don't have.
Something of note that I'm not sure has been mentioned, wasn't in the main post. When you buy one of these cards you have to set it up properly or you're likely to run into issues with it being turned down.
Every card has a URL on it somewhere. (I tend to by Netspend cards, the URL is http://www.allaccessgift.com
). You need to go to the URL on your card and input your information, your name, address and zip code. Most companies, including paypal, check the data given against the data the card holds... if it holds no data on who owns it it comes up as a miss match. Only have to set up each card once
And Netspend cards work fine with googlecheckout, I've used them three times this week. They sometimes do not like Clickandbuy, but they've always worked with paypal for me.