One bit of news from WWDC is that the new version of the OS formerly known as iPhone OS, iOS 4, will be released on June 21st. Along with it will come an iBooks app that will support PDF files. But you don't have to wait until then to get PDF support both on the iPhone/iPod touch and the iPad with an app that looks very much like iBooks.
Fast PDF (US $0.99) does the job for PDF reading; it's a Unversal app (meaning that it looks great on both the iPhone and the iPad). This is really nothing revolutionary, since apps like Stanza (also a Universal app) have been doing this for quite a long time, but the virtue of Fast PDF is that it looks remarkably like iBooks and it is very simple to use.
Just like Stanza, you can download PDF files from either the Internet (this was a bit confusing), from your computer using a built-in server, or via iTunes' file transfer feature. Unlike Stanza, there is no file conversion. Often PDF files imported into Stanza look horribly formatted, and saving the file as an ePub or other file type doesn't make it any better. Fast PDF (which only deals with PDF files) brings everything in, perfectly formatted. After transferring, the resulting file looks exactly like the source.