There aren't any.
That would be a pretty short post though, wouldn't it? Let's go into a bit more detail.
Syl recently wrote about her love for day/night cycles in MMOs and how they contribute heavily towards making her feel truly immersed in a virtual world. Rav then followed this up with some comments about how much she appreciates the changing weather conditions in Lord of the Rings Online, while also noting that this is something that she really misses in SWTOR.
I heartily agree with both of them. I still remember the amazement I felt when I first experienced rain in World of Warcraft (my first MMO), and I'd love it if SWTOR implemented weather and day/night cycles tomorrow. However, I feel that it's a bit unfair to draw a straight comparison between a game like SWTOR and your average fantasy MMO and to accuse Bioware of being lazy for not having all the same features.
Most fantasy MMOs that I know of take place on a single world (things like WoW's trips through the Dark Portal not withstanding). Once the devs figure out how day and night work in that world, how often they alternate and how they change the sky... they are pretty much done. If you add a new area to play through later, it's still going to be in the same time zone and look up at the same sun and moon. (I'd be quite curious about a game that includes different time zones as an in-game feature though, or day/night cycles that change with the seasons.)
In a sci-fi MMO where you hop around between different planets on the other hand, things are a bit different. Every sky is unique, with the differences ranging from a variety of colours to there being different numbers of suns and moons in the sky, so the changes between night and day would be different on every single planet - meaning that day/night cycles would be an extra piece of work that would need redoing every time they add a a new planet.
There is also the question of how the passage of time would work. Right now every planet is forever stuck at the same point in time when you visit - on most of them that's day time, but there are exceptions where it's dusk or night whenever you land. Now, it would be possible to simply tie day and night to the server clock and make it pass the same way everywhere, but personally I feel that it being night on every single planet in the entire galaxy at the same time, wherever I go, would be no less weird than it being the same time on each planet (but at least different on different planets) whenever I visit. So if you wanted to go for something truly immersive, you'd have to come up with unique day/night cycles for each planet - more busywork!
I don't think there are really enough space MMOs out there to establish a shared standard as for how much work should go into features like this, but I did do a quick bit of reading up on how it was in Star Wars Galaxies (which I never played). According to this page, different planets did indeed have different day/night cycles there, based on a pretty simple system - however, it's worth noting that even after eight years of operation, Galaxies didn't have as many different planets as SWTOR launched with.
So I can completely understand that this is not something Bioware chose to go for. At least when you develop a day/night cycle for a fantasy world, players will actually get to experience it most of the time (unless they are in a cave or a dungeon for example). A day/night cycle for Tatooine on the other hand would only ever be experienced by the small percentage of players who actually spend time on Tatooine at that particular moment - and the same would be true for every other planet, with the percentages getting ever smaller the more planets you add and the more you spread out the population. It just seems like a lot of work for a very limited pay-off.
Now, weather... that's something I feel less sure about. I can understand it always being day when I go to Alderaan, but I don't understand why it's always sunny. It seems to be a planet with a moderate climate, so there should be some rain occasionally. And unlike day and night, I could see weather being something that would be easier to "recycle". It doesn't have to be on a fixed timer, so it could just be randomised for each planet, drawing from a pool of existing options that seem sensible for the planet in question (e.g. no rain on Tatooine). Things like cloud cover and the animation for rain (which already exists on Dromund Kaas at least) could be reused on different planets without it feeling weird. (I probably wouldn't want to drink the rain on Hutta for example, but it would be perfectly fine looking the same as other rain.) It would still be extra work compared to just having no weather variations at all of course, but in this instance it strikes me as more of a case of having to put in the work once and then they'd be able to re-use a lot of the assets whenever they add another planet.
So in summary, while I'd certainly love to watch the twin suns set over the Dune Sea one day, I can understand why that's not likely to ever happen in The Old Republic. But a bit of weather? One can always hope.