[gbcdoj]

My question is, is there any biblical indication that certain sexual practices (for example, oral sex) are forbidden between a married couple? What does the bible say about sex within marriage? It would help me a lot if folks responding could cite chapter and verse.

Yes. Gen 38:9-10.

He knowing that the children should not be his, when he went in to his brother's wife, he spilled his seed upon the ground, lest children should be born in his brother's name.

And therefore the Lord slew him, because he did a detestable thing:

Here is an excellent article discussing the Scriptural teaching: The Sin of Onan Revisited.

[AdamSelene235]

He knowing that the children should not be his, when he went in to his brother's wife, he spilled his seed upon the ground, lest children should be born in his brother's name. And therefore the Lord slew him, because he did a detestable thing:

So is ok to spill seed when you aren't doing your brother's wife?

[roylene]

He was struck dead because he disobeyed God's commandment NOT because he was using a birth control method. Under the law if a woman's husband were to die the wife married the brother and their first child would be technically the child of the first husband - God's law. That again was why he was struck down.

[xzins]

The problem with Onan was his selfish unwillingness to help his sister-in-law have a child to continue his brother's lineage and provide for her in her old age. His heart was his problem, not his coitus interruptus.

There is no hint in that passage that the interruption technique would be wrong elsewhere under non-selfish circumstances.