Monitoring solution

Krneki writes: I've been developing monitoring solutions for the last 5 years. I have used Cacti, Nagios, WhatsUP, PRTG, OpManager, MOM, Perl scripts solutions, ... Today I have changed employer and I have been asked to develop a new monitoring solution from scratch (5.000 devices). My objective is to deliver a solution that will cover both the network devices, servers and applications. The final product must be very easy to understand as it will be used also by help support to diagnose problems during the night. I need a powerful tool that will cover all I need and yet deliver a nice 2D map of the company IT infrastructure. I like Cacti, but usually I use it only for performance monitoring, since pooling can't be set to 5 or 10 sec interval for huge networks. I'm thinking about Nagios, but the 2D map is hard to understand, or maybe OpManager. What monitoring solution do you use and why?