Barry
CLAF is a super way to brand standard Oracle and a decent designer will refresh self service with a much more contemporary edge. CLAF is a bit of a black art and Oracle Skins are the only ones I know who do it and do it well.
So as Michael says CLAF is your best start. It won't solve fundamental usability issues (think EITs & absence!) or re-engineer the user experience. Chucking on a nice portal that links off to the standard Oracle pages is a cheaper option than a complete re-skin (which is a brave undertaking!). JLT are using Applaud's EmployeeCenter (disclaimer: I work for Applaud!) as a portal to standard Oracle Self Service functions and they also have a nice Oracle Skin as well.
Building a similar custom portal could be achieved with technologies like HTML5, Flash, APEX or even SharePoint. Oracle will tell you to use ADF (which John Lewis used together with an Oracle Skin), which might work if you've already forked out for the Fusion Middleware licenses or if you're contemplating Fusion Apps Co-Existence any time soon - definitely speak with John Lewis about their experiences.
There are a few success stories of re-skinning. Pfizer in the US re-skinned the whole of Self Service using Flex 3. It was a big undertaking, took a team about a year to do the first part and cost several million USD (and of course there's ongoing support). It looked great but what's staggering are their annual cost savings - USD 50 mil every year! They presented this at OHUG 2011 so there's a slideshow on it kicking around somewhere. I wasn't involved in their project but met with them late last year out of interest.
Blackrock re-skinned Comp Workbench - a big deal in banks, or at least it used to be ;-) That was in Flex as well and was a big win for them.
I'm out of examples. Re-skinning is much bigger in the SAP world - there are several big ISVs who do it.
Whatever you do, use professional designers and UE experts to design - not your developers! I hope that helps.
Duncan