I use vanilla SSH and GNU screen. I have a ping of 150ms to my Linode at the moment and that's absolutely fine. I think above 300 it starts to get a bit hairy. The Vim movement commands are extremely tolerant of a laggy connection, which helps with perception a lot, I think.

Mosh (http://mosh.mit.edu/) could probably improve experience a bit for high latency and/or dodgy connection. Unfortunately, there's no iOS client (yet - https://github.com/keithw/mosh/issues/198). iSSH seems to have it on its roadmap though - http://www.zinger-soft.com/iSSH_features.html.

I started using this after you posted this. I'm Australian (WA) and working over SSH to servers in the US with 230-260ms this tool has changed everything. Very, very nice.