It probably depends on where the majority of your flying is to take place. If you're going to be in controlled airspace a lot and need to work two frequencies, i.e. listen to an ATIS etc, while still keeping a listening watch then two radios would be a very good idea.
Otherwise I'd say one radio would be quite adequate.
There are some radios that have a monitor function allowing you to listen to the standby frequency which is almost like having two radios without the need for an audio panel or another aerial. This might be the best option all round as you can only talk on one radio at a time and covers morno's point about SA without all the extra cost of another box.
Last edited by 27/09; 17th Feb 2013 at 20:09.