Fidelity has a site which lists all distributions. Don't know about Vanguard. But then I don't care as what the heck are you going to do about it??
Well - there are sometimes actions you might want to take. Usually there isn't much to do, but occasionally there is some action that can be taken. It's kind of like tax loss harvesting - it's worth taking a look at for funds held in taxable accounts.
If a fund is paying out a particularly large distribution, you may want to see if the distribution is larger than the unrealized gain you have in the fund. You would take a smaller tax hit by selling the fund before the record date. Then you can decide whether to reinvest in that fund afterwards or do something else once the ex-div date arrives.
You might decide to donate some shares of a fund that is scheduled to pay out a large distribution. If you are going to donate anyway, this may impact your decision of which securities to donate for the year.
I track all the expected distributions at the end of the year because that is a large chunk of my annual income and I like to know the tax consequences. It will also impacts my start of year rebalancing - I like to have an idea of which funds I will be trimming or adding to ahead of time. If a fund has fallen behind and needs to be added to, I may choose to automatically reinvest the distribution. But only if I have determined I have more than enough expected distributions to cover my January withdrawal.
For example, this year I have determined that the distributions paid out should be just slightly below what was paid last year. With some rough calcs I've figured out I can probably get away with paying 90% of expected current year taxes by Jan 15, 2016 rather than the 110% of last years taxes, because it looks like our taxable income will be slightly less than in 2014. I'm certainly not going to pay more estimated taxes than what we paid last year in taxes (so knock off that extra 10% required by safe harbor rules).
My very, very rough estimate based on last years estimated distributions plus other projected income was within 0.26% of the taxes we actually ended up paying.