Alternative To Ping?

I'm trying to use ping to determine if a computer running a monitoring application is running on an external network. Unfortunately it looks like outbound ICMP packets are being blocked somewhere along my internal network. Is there anything else that I could do to achieve this?

If the systems are running up-to-date patches and are clearly all behind a router, I suppose it'd be a safe assumption to say that they don't have firewall apps on each system.

In that case, I'd try to establish a TCP connection to one of the windows services ports, DCOM, RPC, etc, although I don't know which are closed with the patches out now. I'd NETSTAT -n -a to see what ports are open on each box to decide what to test.

edit: I re-read your post, and see you want to check an *external* system. In that case, you may have little to choose from. I'd try to get ICMP allowed on whatever network you are on, or since you are monitoring what are hopefully servers, try to establish connections to http daemon, etc