Emailing photos is probably out of the question for most photographers – most email services do not allow more than a certain number of megabytes. I personally use dropbox to deliver the final photos and share the folder containing their photos with the client, but I realise that becomes unpractical if there is any amount of back-and-forth between you and the client. In that case you need a service with client proofing.
One note about customized flash drives, cd’s, etc.: in some places, digital goods are not taxable but physical goods are, and thus as soon as you deliver your product on flash drives the whole thing becomes taxable… Just something to look into. Of course, if you are delivering prints or if they don’t have internet you don’t have much choice. 🙂
I believe @jamesstaddon uses zenfolio, but there are several other portfolio providers that allow you to do anything from client proofs to online print sales that might be better for you, depending on your needs and your budget.