dotCloud (http://dotcloud.com) supports binding arbitrary TCP ports to your application - and you can easily drop your favorite client implementation regardless of language.

Any VPS host, or EC2, will let you run ZeroMQ in whatever way is appropriate to your problem.

edit: and same for if you run your own server or rent a server, obviously

However, many services won't let you make full use of it; e.g. last year when I tried to get multicast between my EC2 nodes, it discovered it was unsupported.

If you're only using ZeroMQ in tcp or inproc mode, it is nice, but in a pub/sub scenario you are wasting a lot of bandwidth and CPU time.

Can you explain why you're wasting a lot of bandwidth/CPU time in pub/sub?

if you're not using multicast in pub sub, you're establishing individual tcp connections between nodes, it's not any different than doing N point to point communications, whereas with multicast, the data is only copied when needed, your data will fan out if that makes sense with your network topology I think if you look at the picture it'll be clear

http://en.wikipedia.org/wiki/Multicast

But when you have to add the second ZeroMQ (say, two Linode VPSs), how do you secure communication between those nodes?