I'm writing this for my atheist friends who see no reason or justification for believing in God - not to convince them, but to give them a window into my own thought processes, and an alternative to many of the things they've probably encountered.
Most arguments for theism end up suggesting something along the lines of a first cause - that all events come from other events, and following these lines of causation, everything must ultimately come from a single point somewhere. This argument is vividly borne out in the modern picture of the big bang.