I'm working very much with redmine, and I love it!
svn and/or dcvs (Git) support
got it both. if you add the ticket number to the commit message, the commit will appear very elegant in the ticket, this is one of my favorite features as developer :)
document management
got it too, but just very minimalism. You can upload files to tickets and projects (seperately) but you can't search for them (i.e.)
ticketing, bug tracking, wiki
yes, yes and... yes :) I like the syntax of writing tickets or other text contents, kind of similar with the syntax at stackoverflow.com.
multiple project support
of cause you can create projects, sub-projects, sub-sub-projects.... with different access rights if necessary. You can also do this cascading with tickets.
installation and plugins
I have never installed a redmine instance, and I have no experience with ruby. I'm just a redmine user - but I know that it is possible to write own extensions (my company has written one for own purposes, to extend the tracking of time)
Conclusion: I will always use Redmine when I need a ticket system!
Update: Sometimes I am also using the issue integration of code hosters like bitbucket or github. Redmine is the largest solution I've used. Trello is also an alternative, which I like to use to handle customer tasks (you can create teams), when not much people are involved and the project is not that big.
