I used to use as a basis for our standard Database Coding Standard and Guideline
(http://www.nyx.net/~bwunder/dbChangeControl/standard.htm)
+ tried to distill everything else what I have found on the web + "Sybase server Dba survival guide" (it also has naming conventions standards, but it is only very small part of the whole needed stuff actually) + recent Joe Celko's book "SQL programming style". Very important is error handling, found 3 diff.styles.

Actually it would be very good to have it incorporated in some TSQL developer environment. (+ possibility to tune it according to own preferences + good style templates like see for example www.qnxo.com by S.Feuerstein for PL/SQL )).