20+ Free iPhone PSD and iPad Mockup PSDs
Free mockups usually lack in quality, but this collection of iOS Mockups (including iPhone psd & iPad Mockup psds) will give you all of the quality at none of the price.
One of the trickier points of being a web designer is conveying your idea to an existing or potential client. Business owners are generally not a "creative" sort - Visualizing leans right brain, whereas business acumen leans left. In the web design field an entire industry has sprung up around this issue - That solution being a high quality Mockup PSD.