You can get a Ustream and a Livestream app to view most of their content, although they require the broadcaster to make their output mobile-compatible.
I don't know about webcam "sites", but for general webcam browsing, there is an app called iSpy which is great. There's no porn cams or anything, just various webcams from round the world, zoos, beaches etc... You can save cams as favourites, take snapshots, even control PTZ cams.
I use a few webcam sites, and mostly theyre fine on the iPad.
For example this surf site gives you live(ish) view of beeches: Piha Surf Report - Surf.co.nz
While the LondonTraffic site (make a shortcut link to iPad) is great for check out how screwed up the Blackwall tunnel is at any particular time: Blackwall Tunnel | LondonTraffic.org
If you want to view Flash based sites or webcams try PUFFIN browser from the App Store.
This routes your request through a proxy server (in the states I believe) which will 'pull in' the Flash content and then stream it to you in a format the iPad can view.