Thanks all for your inputs.
We're rather looking for some kind of "blackbox" where you just have to plug the sensors, and you can poll the datas over snmp.
We don't really have time for the DIY stuff :)
I think I'll go with the AKCP solution, seems to be the best solution with the widest range of sensors, which are extensible up to 300m.
Looks like a good solution.
@Kirill
With AKCP products, you have an AC sensor wich monitor the AC voltage. Our idea is to check if a power line fails. We already have alarms if our PSU fails, but you can't tell if it's a PSU failure, or the whole power line which is down.
Not entirely what I was looking for, most UPSes support readout of the line state nowdays, so detecting power failure is easy, what we where looking for is a "Energy Counter" at the feed into data center, so we could read out our consumption in kW/h automatically.
Cheers