Hi Ruby
I don't think you should end the debate - don't you find it really weird to see how irrational people can be no matter what you throw at them? I think it's worth it just for the "wow" value
Regarding contradictions - most contradictions in the Bible have some kind of pat, legalistic answer, which usually relies heavily on exploiting abiguity and sometimes sacrificing assumed meaning to temporarily score points (then forgetting that they've 'discovered' a whole new Biblical message the next time you talk to them).
For this reason, I find it much more rewarding to pick maybe just one or two of the strongest contradictions, and never let go (unless they actually are explained away, of course). Sometimes I've been surprised that what I thought was a contradiction, irritatingly wasn't - but in the interests of honesty I pull out after that, often with the rejoinder that I'm unhappy with their obvious twisting of meaning, but that there isn't anywhere else to go with that.
Also, as well as internal contradictions, like those mentioned above, I think it can sometimes be more rewarding to point out where the Bible conflicts with reality, especially if the statement has been made, as it often is, that archaeology always supports the Bible.
One of my favourite examples of this (favourite because although it's suggested as a contradiction by the Skeptics' Annotated Bible I've researched it myself and found it to be uncommented on throughout fundamentalist sites like answersingenesis.org, where often these people get their ripostes, little-used in debates, and fairly watertight) regards Genesis 10 (end) & 11 (beginning), which hold that the whole world had one language after the Flood (which might be expected), and only had many after the Tower of Babel incident. This conflicts with our very clear archaeological evidence of the development of written language, which can be traced pre-Flood (as estimated by fundamentalist Genesis timelines), all the way through the likely dates for Babel, and onwards.
I started that one on
this site (a very very quiet board) - I'm called Doubtful there; it was particularly fun there because I was working with their facts and figures, doing research only when a point was challenged, and slowly realised that this was rather a strong point! A longer version is
here, although I shamefully neglected that and the debate died (I'm Will on that one btw, my real name). But yeah, there's quite a lot of online stuff, which I link to in those threads, to do with the origins of written language (obviously languages were around long, long before, but it's much harder to argue without physical evidence), and it's pleasant because they come from academic sources with no atheistic motivation.
So yeah. Good luck, I think you should stick with it Ruby!