I've been getting a lot of contact from people looking for work as art models. It's getting so frequent that I thought I'd put the info up here for ease of access.
If you're "cold calling", which is to say, sending out an email to someone you haven't spoken to before, present yourself in a professional manner. Modeling is a kind of performance, and performers send a note of introduction that includes their skills, contact information, and a photo. A model is no less a performer. Offering complete information up front projects an air of confidence and experience. Be aware that a photo has 1000 times the impact of an email alone. Even if the recipient isn't hiring immediately, a picture is more likely to stick in the mind and result in a future job. It doesn't have to be a nude or modelling pic, just a nice, simple photo that clearly depicts your face and shoulders is fine. If you have some really unusual image that might help you stand out consider including that if you think it's appropriate, just be careful of the audience you're sending to. An art school might have more conservative tastes than an independent arts group.
Don't forget your contact information!!
The idea is that you're offering something (your unique skills) not asking for something (work). This resonates better on a subconscious level, and makes you seem more valuable.
Be persistent, not insistent!
Do follow up every couple of weeks, even if they don't hire you immediately. A gently reminder that you're available might keep you in mind when something does open up. Don't call too often, though--it comes across as needy and gets irritating, and will work against you.
Specifically for male models: It is unquestionable harder for you guys! Don't take it personally. Experienced artists are comfortable with models of any gender, but less experienced artists may be uncomfortable with male models. You might expect inexperienced guys in a class to be a little put off, but inexperienced girls can also feel intimidated. Don't take it personally, it's not you. Many women who pose have dancing experience, and pose well. It's much less common to find a male model who can pose well, and that's a highly desired talent, much more so than a good physique (the artist can always draw in extra muscles if he really wants to). If you have some unique physical training, do mention it up front, and maybe include a picture of yourself in action doing it.
Also check out my earlier post--some advice for a new model: http://nyfiguredrawing.blogspot.com/2009/02/tips-for-art-models.html
I have a list of all the walk-in classes that I know of in the NYC area (as of about a year ago). It's called Classes about Town, feel free to download it and use it for leads. There are also new classes springing up on Meet up.com all the time.
You can download the list here: http://www.meetup.com/FigureSketching-NYC/files/
Regarding my Summer Sketch Group: I only have 2-3 sessions per month, and I usually hire models I've worked with before, so I don't have too many openings, but I do keep contact info on file, since occasional openings DO come up.
Best of luck,