I just got back from an enjoyable (but expensive) weekend jaunt along the west coast of Sweden and managed to see 2 new WHS. But one of the things that struck me most was how well both of these sites were presented to visitors, and I thought both (Tanum rock carvings and Varberg Radio station) should be commended for really making the most out of their heritage and their place on the list.
I then thought back to any other places that have been really good at this and thought I would just make a quick list of places that have been really good at presenting and interpreting what they have on show, as well as making note of the few that really celebrate the World Heritage Status.

(NB. The list is obviously very subjective, and mostly limited to how the sites present themselves in English, so obviously a little biased on that front. Smaller sites with a particular focus are easier to present than city centres or natural parks so they again will feature more. Also, I guess due to resources, sites in more economically developed countries will feature heavily)

Platinum
Plantain Moretus Museum- The audio tour is the standard by which I judge every other site I visit. No site has done as much to interpret and present its importance as well as this one; made what I thought would be just some average regional museum into a highlight of the World Heritage list.

Gold
Varberg Radio Station – Excellent new visitors centre, beautifully designed to look modern and complement the main structure. World Heritage symbols everywhere! The guided tour really explained how the whole system functioned but also why it is important.
Tanum rock carvings – Museum, visitors centre and Bronze Age farm were of a really good quality. The guide stationed at Vitlycke carvings was excellent at describing what we were seeing and helping to interpret them. But also he was great at explaining different interpretations, and how they have been shaped by different philosophies in modern thinking. The information was accessible but not dumbed down.
Jelling Mounds – really good on site museum that helps explain the site and its significance. Also displaying painted copies of the stones really bought them to life for me.
Rietveld Schröderhuis – the (expensive) tour I went on was very good at explaining the context of the architecture and highlighting the ingenious parts of its design.
(Obviously I am keen on northern European presentation techniques, like I said this is subjective)

Silver
Vicenza – There are maps everywhere on the street, every building that is part of the World Heritage site has an explanation board outside in 3 languages. The tourist information centre had maps showing all the important sites and had walking routes mapped out on it.
Třebic – really not the most astounding of sites, in fact it is pretty dull, however there are maps and notice boards at all the key points and the TIC had lots of booklets on the WHS and the surrounding ones. My experience of the Czech WHS was that they really embrace their place on the list and this was the best of the lot at doing it.
Bru na Boynne (Bend of the Boynne Neolithic sites) – The restoration of the mounds may be controversial, but the management of the visitor experience is very good. The visitor centre was nice and keeping the mounds in a 'remote' setting helps with the understanding of them.
Bauhaus – I think I am biased on this as it is a bit of a specialism of mine, but the tour (in German only) allowed a really hands on experience of the building, this highlighted its functionality which is one of the most important things about its inscription on the list.
Tito Bustillo (Northern Spanish cave art)- The nuances of the tour were a little lost on me as my Spanish is poor, however the guide was still able to draw a gasp from me when showing the main set of paintings and I was able to understand what was being described through the movement of the torch light.

Bronze
Santa Maria delle Grazie/ Last supper – it is a pretty tough thing to keep this painting in a good condition so it deserves credit for trying its best. Also the audio tour was pretty good at describing the painting in detail
Big Pit (Blaenavon) – About the only UK site that seems able to present its industrial heritage in a decent manner, and explain why it is universally significant.
Cahokia mounds – The visitor centre looks a little dated now but it was still a good base. The guided tour was on a cassette with a photocopied map so pretty outmoded as well, but still it helped explain the significance of the site. Also good for having a UNESCO flag flying next to an American flag.
Hypogeuim Malta – limited access but it is well presented and a fairly decent context given

Meltwaterfalls special award for being so nice:
Messel Fossil Pit It was closed for the winter when I accidentally turned up. The academics inside opened up the temporary exhibition centre for us, put on a video, gave us some free books and coffee then drove us back to the station after we had a look around. Really was very nice and certainly not expected.

I keep on meaning to add to this, however after a revisit to Mesa Verde last week I thought I would at least flag that one up.

Gold
Mesa Verde - Cliff Palace The guides on the Cliff Palace tour do a magnificent job of managing a large, non specialist crowd alongside explaining the basics, giving the site context within contemporary thought, the success and failures of the National Parks Service management of the site and its relationship with the indigenous community. The two tours I have had of it really were surprising in the lengths they went to fully communicate a wide range of concepts to the tour groups.

Having said that the tour of the Balcony House was a little frustrating, with around 50% of the time being spent talking about the physical aspects of the tour, which to be honest weren't that tough and could easily be summed up as: "If you don't like heights, ladders or confined spaces probably best not to do this tour."

Haha, is this a feature request? Was thinking about that myself :D

Mesa Verde is pretty great, I agree.

Mesa Verde is a really impressive site, and I loved their tours. Sorry your visit to the Southwest corresponded with an abnormally strong heat wave; hopefully there will be some relief soon.

As for some gold stars in the Americas, I thought Xochicalco in Mexico had an excellent visitor center and very good displays around the ruins. I was also very impressed with the guides and the displays at Ingapirca, a component of Qhapaq Nan, when I visited Ecuador earlier this month. I'm also still rather fond of the museum and the tour of the Viking ruins at L'Anse aux Meadows in Canada. In the US, I'm partial to the great national parks that are World Heritage Sites, since each park's visitor center has helpful rangers and guides to trails and natural sights throughout the parks.

Yep it was pretty warm, especially for a northern European, fortunately with family in the region I had some helpful nieces and nephews to drench me on water rides and at aqua-parks so I was able to cope :)

Yes - water parks are a great way to beat the heat! Hope you have a good trip out West (and if it gets too hot, the weather is a lot more comfortable at the Redwoods or Olympic National Park on the Pacific Coast right now).