MTR is a useful command-line utility which combines ping and traceroute to display the path packets are taking between two machines.

I've compiled mtr-0.71 it for Mac OS X, and you can get it here: mtr.zip.

The zip file contains a universal binary, a man page, and a README file telling you what to do with them.

If you like this, you might also like my ports of wget and bacula-fd.