Have you closed all apps by double clicking the home button, then holding one of the apps in the tray until it wiggles, then touching the red minus on all icons? Still open apps take up ram so that there may not be enough for the web page.
When was the last time you powered completely down and restarted? I need to do that about once a week to keep it zipping.
Also, is it JB and if so what, if any tweaks do you have running. If or if not, did you notice it slow down after a particular app got installed?
Actually, I tried one site: cnn.com and it gave me the message that it the network wasn't connected. Suspect that we changed a setting somewhere. No pages will load. Probably will go to an Apple store and hand it to them to "fix".