Here's a rational argument for God, drawen from the Cosmological Fine Tuning discussion. Using cosmologist Paul Davies' numbers for the likelihood of the universe having arisen by chance Forster & Marston (1989) set out the Bayesian analysis as follows -
Let us assume the existence of a deity is one in a million.
Let us assume the chance of that deity creating the universe as is is also one in a million.
OK, so
1.Prior probability: Pr [God exists]: = 0.000001
Prior probability: Pr [No God]: = 0.999999
2.Prob [universe inhabitable if God exists] = 0.000001
Prob [universe inhabitable if no designer] = 0.00 (one billion, billion, billion zeros) 1]
THEN: Prob [God exists given that Universe is inhabitable]
Prob [universe is inhabitable if God exists] x Prob [God exists]
= -----------------------------------------------------------------------------
{ Prob [universe is inhabitable if God exists] x Prob [God exists] }
{+ Prob [universe is inhabitable if no God exists] x Prob [No God] }
0.000001 x 0.000001
= -----------------------------------------------------------------------------
{ 0.000001 x 0.000001 }
{ + (0.999999) x (0.00 (one billion, billion, billion zeros) 1) }
this gives us a figure so close to 100% as to seem to establish beyond doubt the reality of God (but see below!)
Now we can clearly change our initial numbers for a deity, or use another cosmologists calculations (they are all similarly huge though), but this in a nutshell is the problem. I have pointed out all kinds of answers which do not require God can be produced, from multiple universe, to constraints, etc, etc
The Skeptic article I often link is excellent
http://www.skeptic.com/the_magazine/featured_articles/skeptic13-2_Kuhn.pdf
and I'm not saying this proves anything at all -- it merely demonstrates why there is a problem, and why invoking design for the universe is not actually at all irrational. If one has a vast multiverse of universes he problem is greatly reduced but we can't show it is so yet.
So you can still argue, if you so desire, a logical case for theism. Another more playful example of mine can be found here --
http://www.internationalskeptics.com/forums/showthread.php?postid=4242735#post4242735
Anyway night all, and Happy New Year!
cj x