The DSM book is not online without high cost but just the codes are available from several places

Note that the DSM is fully copyrighted and protected. Seek permission from the publisher, the American Psychiatric Association before reproducing any of it.

DSM-IV Diagnoses and Codes, Alphabetical Listing
http://www.dr-bob.org/tips/dsm4a.html
and
DSM-IV Diagnoses and Codes, Numerical Listing
http://www.dr-bob.org/tips/dsm4a.html

The complete list of DSM-IV Codes in both versions is available here:
http://www.psychnet-uk.com/dsm_iv/_misc/complete_tables.htm#Name

BehaveNet Clinical Capsule
Organized by Axes all the codes are here but the interface is very busy and requires a lot of reading before you find what you are looking for.
http://www.behavenet.com/capsules/disorders/dsm4TRclassification.htm

ICD9Data.com
All the codes are here but hierarchically arranged so you have to click through a few layers. This listing contains exercpts from textbooks and the entire index listings for each diagnosis and so give TMI (Too Much Information) for mental health treatment purposes.
http://www.icd9data.com/2007/Volume1/290-319/default.htm

Flash Code
All the thousands of codes are here. We want 290 to 320. You will have to click through several levels to find the codes you want to use. The meanings of the buttons is not obvious and requires some learning.
http://www.icd9coding1.com/flashcode/userRegister.do

ICD-9-CM
A table in numerical order and two levels deep (not a simple list as is my Reference List to  ICD-9
http://www.dmi.columbia.edu/hripcsak/icd9/
The alphabetical listing is too large to be usable as it covers all diseases of any kind.

eICD by Yaki Technologies
Free registration required and the diagnoses can be several levels deep.
http://www.eicd.com/EClass/5.htm

ICD9 at Chrisendres
It is all here but again takes some searching and time.
http://icd9cm.chrisendres.com/index.php

The Center for Disease Control
It is here but too complete for everyday use in mental health practice.
http://www.cdc.gov/nchs/datawh/ftpserv/ftpicd9/ftpicd9.htm#guidelines