I either use "transgender", or trans*. The asterisk, in a nutshell, is an acknowledgment that there are many types of trans identities, and aims to group them under the same non-cis umbrella (for certain purposes). So, transgender and trans* do not always necessarily mean the same thing. Anyway, I find "transgendered" to be problematic mainly because it is not a verb, it is an adjective and an identity, not something that you do to yourself or that happens to you (though others may disagree). I've heard other arguments that I'm not very good at articulating, but I was wondering what other people thought.