What is the actual construct you are interested in?

Mental health/Psychopathology, Resistance, Resilience, Outcomes, etc?

See Tate, R. (2010). A compendium of psychological tests, scales and questionnaires. Madison, WI: Psychology Press.

Maybe the Self-reporting Questionnaire.

Beusenberg, M., Orley, J. H., & World Health Organization. (1994). A User's guide to the self reporting questionnaire (SRQ).

It is widely used 

http://apps.who.int/iris/bitstream/10665/61113/1/WHO_MNH_PSF_94.8.pdf

I agree with David -- we would need to know more about what you're looking for. There are validated scales for depression (Beck, Hamilton), anxiety (Spielberger), addiction (MAST, DAST) etc.  Once you figure out the constructs you're looking for, you can find the measures.

Check out SCL90-R. Gives a general overview and subscales. You can see in the overview how many answers have been marked positive and their intensity as well. Another one is the Brief Symptom Inventory. But I have no experience with that one. May be it can be obtained for free in the Internet.

 What do you want to measure? Detection? Results? There have already been good sugestions of scales for detection. Concerning outcomes ,I would suggest quality of life. Try whooqol, from WHO. Open access. 

The Warwick-Edinburgh Mental Well-being Scale (WEMWBS) measures positive mental health and has been used in prison populations, clinical samples, males, females, adults of working age and older people. It comprises 14 positively-phrased statements and uses a Likert scale. It is a self-report tool and has been adapted and validated for use in other countries. In England the shorter version is used at intervals with individual patients from the point of entering a community mental health service and throughout treatment.

Others have given you some good leads on short scales for limited screening.  Measuring response to treatment may be different than screening tools for symptoms, however.  One instrument that you may want to consider is the Burns EASY diagnostic system.  The questionnaire is about 50 pages and is a good tool for screening and diagnostic hypothesis generation.  It is not public domain, but the price (about $150 USD) is reasonable for a perpetual license for unlimited clinical use.  If you want to use the scales for research purpose, you would need permission from Dr. Burns.  I do not know whether you can negotiate other financial arrangements for clinical use of the scale, but contacting Dr. Burns at the following may be helpful.

[email protected]

Here is a brief description of the scales and an order form, if that interests you.  I use this instrument extensively as part of my intake for nearly every patient and I've found that it saves much interviewing time an allows me to be more focused in the intake and evaluation process.  See the following:

https://daviddburnsmd.files.wordpress.com/2015/10/aaa-easy-order-form-version-4-website-2015.pdf

For general clinical use as a diagnostic self report screener for psychopathology, I know of nothing better.  In actual practice, you might supplement with other specifically tailored scales.  This is a pretty good substitute for a SCID (Structured Clinical Interview for the DSM.)

Mental health usually refers to mental illness.  If you are interested in mental health, you might do better to look at quality of life scales, strength scales, or other elements drawn from the positive psychology field.  Best wishes!