Tools to help figure out optimal setups?

What kinds of tools do people use to figure out optimal setups? (short of setting up a test network that duplicates your real one) I currently am using the usual, ping, traceroute, wireshark..

Dia is nice for drawing pretty pictures. Is there anything like dia which also does simulation or sanity checking which is also free?

Im just a new user but I think there is a DUDE application that is free for MT and has lots of special powers.

I think GNS3 is what your after!

Lower end devices are cheap enough to buy multiples of and RouterOS is used across the board so I almost always have a test setup doing something weird, funky or testing new ideas.