80, 443 for HTTP/S, and 587 for a VPN service. Reason being that I travel frequently, and often have to connect through a bunch of different networks, Airport WiFi, mobile roaming, hotel WiFi, etc. and you never know the kinds of network restrictions they impose on their pipes.

80 and 443 is least likely to be dropped, while 587 is a common SMTP port that could make it through most networks.