Just saw on the Linguist List about a browser based syntax tree generator available here: http://mshang.ca/syntree and the linguist list article: http://linguistlist.org/issues/23/23-920.html
I tried it out and it is fairly simple to use. I haven’t integrated it in any other programs yet, just a quick trial. During my MA days, I mainly used the tree form program that was suggested in LING 3340 Grammar and Morphology that Joshua Jensen taught: http://sourceforge.net/projects/treeform/
It was a bit quirky at times but worked well enough to copy and paste into MS Word for weekly class assignments.
Since I dusted off LaTeX recently, I at some point I am going to try making trees in it and will post about that. Feel free to let me know what people are using for this.