When I first bought my Four-Thirds equipment in 2004, I bought the Olympus E-1, the 50-200mm f/2.8-3.5 and the 14-54mm f/2.8-3.5, all of which were weather-sealed.
Later in 2004, not satisfied with doing indoor sports and photos of flowers and animals and birds, I put myself and my equipment outside in three hurricanes. Shooting in 75 mph winds is incredible, especially when rain is hitting you and reminding you that you can be hurt.
|Olympus weather-sealed lenses are amazing|
After each hurricane experience, I would go inside, and dry the equipment as much as possible and let it sit for a while before returning to the weather. In numerous occasions since then, I've used my 50-200mm lens and Olympus E-1, especially for cross country. It was only in late 2011 when it ceased to be my primary camera body, and an E-5 started to be. The 50-200mm serves me regularly in outdoor sports, and can even be used on the Panasonic GH3, also weather-sealed, through a weather-sealed adapter.
I can't imagine taking out any other specification of equipment. I have a Leica/Panasonic 25mm f/1.4 lens that was meant for the Leica Digilux 3. It's quite sturdy but lacks the weather-sealing. Considering that it was about the same price as the 50-200mm, it seems odd that it's not sealed but it is a Leica lens, even if it was supposedly hand assembled by Panasonic instead of Leica at about 1/3 the cost.
Seeing as how Nikon has embraced the ocean with their Nikon 1 AW1 and so many others such as Pentax are putting more of their lines into weather-sealed equipment, will the third parties finally do something?
As far as I can tell neither Sigma, Tamron, or Tokina have any weather-sealed lenses. That would be a shame, especially with the Bigma 50-500mm lens. To me, any lens priced at over US$500 should be sealed. I'd hope that more companies would take care of it. Can you afford to take your best equipment (or your only equipment) into a storm?
Update 2013.11.27: I'd love to take advantage of some of the lens deals out there. The Olympus M.Zuiko 45mm f/1.8 looks a treat, and with a discount, even better. However, the moment it's wet and stops functioning, I'd have to buy something else to replace it. Similarly, the 75mm f/1.8 is great but could be affected by bad weather. Within micro Four-Thirds, there are 5 weather-sealed lenses now: Olympus 12-50mm, 60mm macro, Panasonic 12-35mm, 35-100mm, and Olympus 12-40mm with the 40-150mm arriving in 2014. I did everything with 3 lenses for years, though 150mm is not quite 200mm (40-150mm f/2.8 vs 50-200mm f/2.8-3.5), so I can't reach as far, although there is supposedly a 1.4x tele-converter due in 2014.
Update 2014.12.14: It's been over a year since my last update. Pentax seems to be the least expensive way to get weather-resistant camera bodies, with the K-50. They're also good enough to mark their lenses with WR to signify weather resistance.
micro Four-Thirds hasn't gained much ground. The E-M5, E-M1, GH3, and GH4 are all weather-sealed camera bodies, but the number of corresponding weather-sealed lenses is still minimal. The Olympus 40-150mm f/2.8 has been released, as has its 1.4x teleconverter. Yes, the teleconverter works with only one lens as of now.
That said, Olympus have a 7-14mm f/2.8 ultra-wide angle lens, along with a 300mm f/4.0 super telephoto lens scheduled for 2015. A number of Four-Thirds lenses are still available, which work reasonably well with the E-M1 and GH3 and GH4 using auto focus.
As I'm now getting into video, I'm looking at certain adapted lenses that are not weather-sealed. While this area is in drought, that's generally not a problem but for dust. Someone recommended the Sigma 18-35mm f/1.8 lens with the Metabones (essentially a reverse tele-converter) Speed Booster adapter. This is supposedly a great lens but the ART series lenses are not weather-sealed.
Update 2015.04.29: I recently added the Pentax K-50 to my bag. Both the body and the 18-55mm f/3.5-5.6 kit lens are weather-sealed. It's a good, low cost option if you're on a budget. I don't have any other lenses for it, so I should pick carefully, but one of the lenses that has been on my list is the Sigma 18-35mm f/1.8 ART lens, which is not weather-sealed. I have a hate-hate relationship with Sigma but they've come a long way in the last two years. I'll probably buy their USB dock also, so I can fix the front/back focus problems that they usually have.
Otherwise, I could buy the Pentax 16-50mm f/2.8, which is a sturdy, reliable Pentax lens but that maximum aperture means a lot and if I'm more concerned about getting the shot indoors or in lower light, the Sigma would be better, even though its focal length range is very limited. The Pentax lens is better overall.
Olympus has an 8mm f/1.8 fisheye lens that will be available this summer--which likely means September 30th. It will likely be the first fisheye lens I'll ever own, and since it is weather-sealed, it will be useful not just for skate parks, but for beach and bad weather photos too.
Update 2016.04.03: I gave away the Pentax K-50, and since then, I bought a Nikon D7200. I've now got three lenses, none of which seems to be weather-sealed.
Sadly, I've been learning that outside Olympus, weather-sealing is not quite as comprehensive. It seems that a lot of products are given a gasket to keep liquid from entering the camera body and perhaps, a fluorine coating on the frontmost lens element to resist liquids. I would hope that there are also gaskets around zoom and focus rings, etc. but it doesn't sound as though it happens.
Considering that lenses last longer than bodies, why not do more for the lenses?
The Olympus 8mm f/1.8 fisheye lens is well built. I'm thinking that it is as weather-resistant as the 12-40mm f/2.8 and all of the Olympus Four-Thirds SHG and HG lenses.