Dear Wills,
Oh, the joys of parenthood. Believe me, it's all down to annoying mummy. It's part of being a pre-shooler, I think. Also, it's universal.
Very familiar problem, this. My dd, now nearly 4, has been like that for ages as well. It used to be easier when dh dressed her, which he did especially in the last months of my 2nd pregnancy, but mainly she was being good because it was new and therefore interesting. Now that the newness has worn off she is just as annoying with daddy (phew, what a relief).
I have found a few things that work for us: first of all I give her several options for clothes (would you like to wear this shirt or that?). She'll forget there is also the option of not dressing at all.
She can also choose if she wants me to take off her pyjamas or wants to try it herself. Sometimes the teddybear or one of her dolls helps (including funny voices...)
Also, we use the cooking alarm (there's probably a better word for that, but sorry, I'm Dutch, so I call it a kookwekkertje), I ask her how many minutes she thinks she'll need before she wants to get dressed. I usually suggest four minutes, after which she will say, no, she'll need at least 3, or she'll hold up two hands and I'll enter 5-7 minutes on the alarm, depending on how much time I feel we have. After the alarm has gone beep we'll (try to) start to dress.
If she won't put her foot forward to put on her sock I usually ask her if she remembers which is right or left. She's very proud that she knows now and will forget she was trying to annoy me.
With eating breakfast (which is also a problem with us) I give her the options of eating herself or me feeding her.
The big trick is also a very difficult one: try not to get cross. Pretend you're happy (I'm usually at my worst in the morning, so it takes considerable effort) and be determined not to give in.
Sometimes, however, none of the above helps & I'll just end up shouting at her or leaving her to watch tv for 5 minutes or eat her breakfast (or both) to see if it goes away. The things we do to keep the peace. George W & Saddam could probably learn a lot from us mums.
Good luck, I know how you feel. You're certainly not alone if that's any comfort.