Centralized Pub Sub options that do not use cloud based resources

Are there .Net compatible Pub/Sub tools out there that are centralized, but don't use any cloud based offerings?

I have looked at NServiceBus and it is the Pub/Sub front runner, but I don't like the amount of infrastructure it puts on each machine.

I would prefer to have a centralized option where I have a beefy server that handles all publish and subscribe actions and simply makes the needed calls when a publisher sends a message that a subscriber needs to get. (Kind of like Amazon's messaging service.)

I could wrap NServiceBus up in a system like that, but I would rather not do that if there is a good solution out there already.

In case you are wondering why I said "no" to the cloud option, I work for a medical company and the issues of sending Protected Heath Information over the web are just not worth the benefits of offloading this to the cloud. Also, if it goes down, I need it to be our fault and have the fix be under our control.

(NOTE: I am looking for solutions in the under $10,000 range. Things like Tibco are great, but they are just out of my price range.)

You're looking for a message broker, which isn't generally the direction that ESBs have gone since the broker becomes a bottleneck very quickly in a high throughput/availability scenarios. MassTransit is an alternative to NServiceBus, as is Rhino Service Bus.

I am personally waiting until ESB frameworks start coming out that either have a pluggable framework for their messaging architecture or are built around ProtoBuf or zeroMQ or RabbitMQ. Anything but MSMQ. Mass Transit should have RabbitMQ support sooon(tm)...