Some programs I use to display trees in OSX. Some allow the user to modify trees.
TreeViewX: the industry standard for simple tree visualization.
TreeEdit: views and manipulates trees, re-roots, simulates trees.
FigTree: nice graphical tree viewer.
TreeIllustrator: not only it displays and fiddles with trees, but also has a built-in ToL browser/search engine.
TreeStat: calculates tree statistics (balance, shape, length, popgen).
Phylodendron: draws trees on a webserver or locally (Java app).
TreeJuxtaposer: displays and compares/compresses trees. needs GL4java.
ArboDraw: tree editing with sequence annotation functionality.
TreeMaker: builds taxonomies with species richness data.
TreeSetViz: visualizes tree sets in treespace as a Mesquite module.
notes on evolutionary biology papers/programs and other stuff: a non-frequent approach