Edmund,
The bible isn't one book. It's a collection of many books, written by many different authors over several thousand years. Religious and a-religious scholars agree about that, although obviously differ over whether they were divinely inspired or not.
Warnings against other gods are scattered throughout the Old Testament (the books written from around 1400BC to 400BC).
Specifically and from memory rather than looking up chapter and verse, beyond the commandment "you shall have no other gods before me", there are warnings against worshiping Asherah, Baal, "household gods", Molech. Possibly others. Whether or not you see those named as gods, demons, twisted fantasies designed to keep others in line, they are named and both warned against, and repeatedly worshipped against Yahweh's express command.
In the New Testament, (books written in the first hundred years or so after Christ), reference is made to Aeres - the Greek god of thunder and war, and warnings against various other Greek temples and the practices associated with them. Take a look at Acts if you're interested.
Later on in the early church you've got massive exposure to other gods when Christians or "followers of the way" refuse to worship the rulers of the day as gods. Named and unnamed, it's a recurring theme throughout the history of the church and the "chosen people" before Christ.
IF you're looking for sources outside the bible, I'd take a look at Tacitus - he certainly wasn't a fan of Christians or Jesus! Or else have a look at Josephus, although as a Jewish scholar I suppose you might find his adherence to massive and abrahamic tradition annoying. Tacitus though as a Roman comes from a totally different perspective.
It doesn't matter though. The best collection of evidence I have is my own personal experience; I know that I am talking to someone who is both fully human and fully divine, but I'm sure the more I mention him the more irritated you are probably getting with me. And it isn't my intention to irritate (or to convert), I just wanted to put forwards my own alternative experience.
I wish you well.