We get weekly reports on what the top 10 selling products in the online Apple Store are. In the last week of March the 16GB iPhone took the lead by sales amount and items sold.

The 2nd spot is held by the 8GB iPhone.
The Apple iPhones can now be had with the new unlimited AT&T plan that gives you unlimited minutes in addition to unlimited data for $119.99/month.
If you do not need 3G connectivity or live in areas where you do not get 3G than not much speaks against buying an iPhone these days.
T-Mobile in Germany announced yesterday steep discounts for the Apple iPhone. It is hard to say if AT&T would be doing something similar. T-Mobile cuts iPhone prices by up to 300 Euros. More details.

The iPhones sold on the Apple store ship in 5-7 business days for $399 (8GB) and $499 (16GB).
More details on the Apple Store.