why not just take a look in the Ultra/Adventure racing section of the forum - enough challenges in there to keep someone happy for a while
if you want ultras, then look no further than the Ultratrail du Mont Blanc (UTMB) - generally reckoned to be the ultra equivalent of Kona IM. hard to get into and bloody hard to finish. there are tougher ultras in Europe like the Petit Trotte du Leon (UTMB on steroids), of plenty of long UK ones like the Thames Path
MTB races - start with TransWales, move up to TransAlps and the onto TransRockies
If your swimming's improving why not look at a SwimTrek holiday or some of the long challenges like Lake Windermere or the Channel??
as Meface suggests, step back from long distance and see what improvemenst you can make over short. that can be hard wor
or try something new - mountaineering, paragliding, kitesurfing, rock climbing, ski touring as examples
you really are only limited by your imagination, time and money.
Edited: 26/06/2012 at 09:56