I haven't used foreflight, but I do like Skycharts Pro. I had the regular iPhone version, which the author stopped development on Skycharts at v1.6, then continued with Skycharts Pro that is universal (up to version 1.9.)
One interesting thing is that Skycharts has experimental support for a Posimotion G-Fi, which should allow GPS without having a 3g iPad, and doesn't require any jailbreaking of the iPad. If it works, it should allow GPS without worrying about positioning the iPad with a view of the sky, and also work in airplanes that don't have a cigarette power plug (which all of the stand alone GPS antennas, such as the tom-tom require, and lots of rental aircraft are not equipped with.)
Skycharts doesn't have the flight planning of foreflight however, but it does allow downloads of L charts (with all the airports plates on that chart), Sectionals, & TAC charts.
I wrote the makers of Foreflight to ask if they will have G-Fi support as well, haven't heard back (but I just emailed them today.)
(Of course, a better solution would be to allow either plug in or bluetooth GPS units to act as if they are native, but apple doesn't allow that. I checked around the internet, and bluetooth GPS is not currently part of the beta version of the iPhone OS 4.)