I've been working on the 'Panic & depersonalization' handouts list in the Good Knowledge section of this website.  The list contains most of the handouts and questionnaires I currently use when working with people suffering from panic disorder, agoraphobia or depersonalization/ derealization disorder.  Here they are with brief descriptions: 

Panic disorder severity scale (PDSS) - the main scale I use to assess initial severity and track progress. 
Diagnosing panic attacks, etc - I will sometimes sit down beside the person I'm working with, show them these diagnostic criteria and clarify which symptoms they suffer from and which they don't ... and then come to a diagnosis.
Vicious circle & maintaining factors - I often print this Powerpoint handout out (2 slides to a page) to use as a handout and also to clarify why and what we're doing in therapy.
Interoceptive symptom induction tests - again, I use this to remind myself of standard 'interoceptive' challenges.  Can be helpful when fear of catastrophized internal sensations (e.g. feeling faint/might have stroke; heart palpitations/might have heart attack, etc) seems an important part of the symptom picture.  These tests can then be used to clarify anxiety pathways and also as desensitization/exposure/behavioural experiments. 
Depersonalization scale, scoring and background - good for assessment and monitoring progress. 
Panic attack diary page 1 - this diary format (both pages) can be useful for gathering lots of relevant information about symptoms, triggers, avoidance and so on. 
Panic attack diary page 2 
Paired word exercise - a classic test.  If reading through these paired words induces anxiety/panic in a sufferer it can be very useful in helping them see how their catastrophic interpretations are a key part of the problem.
Catastrophic beliefs questionnaire - again can be useful in assessment and monitoring when using a CBT approach for panic disorder.
Panic rating scale (PRS) - I tend to use this scale particularly to clarify safety seeking behaviours and catastrophic thoughts. 
Agoraphobia assessment and scoring, Ost - a scale I use a lot as an initial assessment, to guide desensitization/exposure/behavioural experiments and monitor progress.