Best tools for network toubleshooting?

Hi,

I am looking for any hints about tools used by more experienced members here. I am not hard core network geek so GUI based tools are proffered (and freeware) - for Windows and Linux platforms.

What I already know and use:

• Wireshark - pretty obvious :-). I am using F5 plugin but wonder what other plugins are really useful in real life work?
• Ostinato - seems to be very nice packet replay and crafting tool - will have to figure out how to replay captured traces but even without this knowledge it's very promising
• Network Emulator Toolkit (Windows) - seems that it would be great for simulating different type of links (like changing RTT, packet loss, etc.) - just installed it and have no chance to play around.
• TCP/IP Builder (Windows) - simple yet very useful tool to play with TCP/UDP connection setup
• netem (Linux) - exception from my own rule - command line tool - but seems to be quite powerful in the same area as Network Emulator Toolkit

Piotr