GR, an explanation of how the text, structure and history of the 4th Amendment shows that it is best interpreted as two separate clauses, and thus not requiring warrants in order for a search be deemed reasonable, may be found in pages 3-13 of the following PDF: http://islandia.law.yale.edu/amar/lawreview/1994Fourth.pdf
Perhaps it won't convince you, but I think you'll at least find the history and analysis interesting.
If you're interested in this and other issues of interpretation of the 4th Amendment, and have an hour to spare, read the whole article (it's 67 pages).
BTW, I know that I'm in the minority when it comes to the Warrant Clause, but I'm too much of a textualist to believe otherwise. (If you can find the old Kelo threads, you'll see that I similarly make a textual argument that the 5th Amendment does not require courts to determine whether a taking is for public use, but that a whole other matter).
FReegards,
AuH2O