Sym
Takes any selected objects and instances and mirrors them across the x axis in one button press. A very simple script - I wrote it primarily for people like me who are modeling cars - buildings - helicopters - whatever - and want to build everything on one side and then make frequent previews of what the model will look like with both sides (and who don't want to click on many buttons).
For a max 5 - 4.2 version of this script - please download bspack_r4_r5_v031.zip. Use the original bspack_r42.zip if you want only max 4.2 compatibility.
The only major differences between script packages are slight version compatibility issues - there are no new scripts added between the 3 packages.