To throw in another consideration factor, it is rumored that the new OS Snow Leopard might be released this year (nobody knows exactly when of course). Though the preview was announced and developers were given access for their developing of software compatibilities. Remember, new OS will be loaded in all macs when it is officially launched. If you get your macs before these launch, its obvious you goto purchase the OS thereafter.
Yes, getting a mac (more so macbook/Pro/AIR) consists of accessories that might be useful to get too. But agree with the rest that prices of the machines should not vary much. Instead if you're looking for more discounts etc, you should look at education/Employee purchase program discounts or better still, friends who works with the apple retailers (but even so, not everyone will be able to get at staff rate).
But having said all that, it'll always be in a waiting game when it comes with technology, get what you need, when you need it.
All the best in your hunt for that mac! No regrets!