If we put our child in their crib at night to go to sleep, is it
healthy to allow the baby to cry because they want attention or want
to sleep in our bed. Our son is 9 months old, research and article
links would be great

Go buy the book: babywise

IT was a lifesaver for wife and I, answers all questions.  And yes, it
is okay to let child cry, it hurts our hearts but not theirs.

-Clint

Here is a review of many different techniques for dealing with
establishing good sleeping patterns, Interventions for Infant and
Toddler Sleep Disturbance: A Review, at
http://www.tau.ac.il/~sadeh/baby/kuhn.html.  It was originally
published in Child & Family Behavior Therapy and is very well
supported by many good references.  Check out the section on
"extinction" and "modified extinction" in the behavioral section- it
describes extinction techniques(letting a baby cry), and thier
effectiveness, and you can see at the bibliography at the end where
the information is from.

My wife was told by her doctor when she was worried about something,
"Just love them".   And she did, and they turned out okay - well
except my son likes to wear dresses and funny hats....  :)  (Do you
know how mad he'd be at me right now.... HaaaaHaaaa)

Oh my goodness....it definitely does affect a baby's well being to let
them cry!  It sure does hurt their heart! Crying is a baby's way of
communicating..responding is what leads them to feel content and
secure about the world, including the people who care for him.  READ 
Nighttime Parenting by Dr. Sears.  Excellent book.

I slept with my babies (including a set of twins) and gradually would
move them to a bed right beside my bed.  My mattress is on the floor
and I put a youth size mattress on the floor and after the baby or
babies were asleep I would put slide them over on to the mattress.  I
could check on them and comfort them from the comfort of my bed. 
Eventually, all of my children graduated to their own rooms quite
easily and successfully.  You will never regret being there and
comforting your child at this early age...they grow so fast and what
other time and place can you provide the comfort and security and
physical closeness a baby needs than to be there for them at night. 
Mine looked forward to a 'big kids' bed and their 'own room'.  It's
alright to follow your instincts.
A mother of happy, contented and snuggled kids