Read the full text of the propositions here.
Proposition 19 - Yes

Proposition 20 - A Shaky No

I did like that this bill had a couple wording changes making the law clearer, but overall, these minor changes weren't enough to change my mind.
However, I'm not really confident that I know a whole lot about the consequences of this bill. I just figure if I'm not sure, I'll vote no because the whole proposition system is absurd anyways. But that's another subject I could spend ages on...
Proposition 21 - Surprisingly a Strong No
I am very supportive of the main idea of this bill that is represented in its brief description. The reason I'm voting no on this is the fact that the bill also (read it) takes almost all entrance fees to state parks. I wish I could just take that part out of the bill. Then I would vote for. While, I think it's a wonderful idea in theory, in reality, I think that taking away entrance fees will only encourage obnoxious underage teen drinkers and other troublemakers to use the parks as their partying grounds and their trash cans.
Not that I'm against drinking ... actually my law school inspired alcoholism is very near and dear to my heart, but I think it's much better if people make a commitment to go (the fees at most places are already incredibly affordable) say hiking or BBQing etc. than have people stop by every time they want to party away from public places where police officers can show up anytime.
Proposition 22 - No
The fact of the matter is that most of our highway upkeep, education system, and so many other programs that everyone enjoys the use of come from the state government rather than local governments. Of course our state government has a terrible name, pretty rightly so in most situations, but, for example, our UCs need funding a heck of a lot more than local community centers that no one will ever use.
Proposition 23 - A Very Very STRONG NO
I really hope that this needs no explanation. If any of you have been in L.A. during smog season, I'm pretty sure you'll understand the necessity of keeping air pollution control laws! Besides for anyone who thinks that this may save them money, "major sources of emissions" = big businesses. But really it comes down to if you give a damn about our planet, and if you don't my opinion surely won't change that.
Proposition 24 - A Strong No
This is another bill whose description is incredibly misleading. This bill is about a particular type of tax deduction called specific net operating loss. This is a classic tax deduction allowed by the IRS, as well, and reflects deductions that individual people can take. If a person has net losses in one year, they can usually use these losses to counteract the gains they have in a following year in order to reduce their taxes for that second year. This bill takes away similar allowable deductions for corporations, including small businesses. Furthermore and very importantly, we have already almost eliminated this type of deduction which should be allowed to businesses like it is individuals. The current law already only allows specific net operating loss deductions for one year in, I think it was every three years. I don't remember exactly (I read all these bills about a week ago, so I've forgotten the details.)
From the description on the ballot, I bet this will pass, but I think it will have a tremendously negative effect on the attractiveness of California for business (and thus employment opportunities), including small businesses.
Proposition 25 - Yes
While I'm generally pretty hesitant to vote for constitutional amendments, this one seems like a necessity, particularly at the moment. I saw this fabulous article in the Wall Street Journal that made fun of the California legislature for passing massive amounts of ridiculously minor bills while it still can't agree on a budget. Besides, my mom's voting for it, and that's pretty convincing in my book.

Proposition 26 - A Strong No

This is pretty absurd. First off, it's a constitutional amendment, a fact that I wish would make people immediately skeptical. No one wants to pay taxes, but this could be disastrous. We're already in a financial crisis and Proposition 22 will probably pass preventing the state from getting money from local governments. Where do people think the money for our world-renowned universities comes from? Our highway repairs? And so much more. We need to deal with our budget deficit and, lets face it, to do that certain taxes are necessary. Otherwise, there will be a heck of a lot more people fleeing California, like me, and an ever increasing percentage of unemployment. Nothing sums up my opinion on this matter like this amazing Berkeley professor's "Letter to [his] students."
Proposition 27 - I have no idea, but possibly no
At first I wanted to vote yes on this because I'm not convinced that a redistricting committee won't become the property of the wealthy. But ... really, I think in theory a redistricting committee is a good idea, and I have absolutely no idea the effect of this. Besides, I got burnt out before I could read the full text of this bill, and reading the bill probably won't tell me anything about its possible consequences. Who know, maybe I'll resort to a coin toss on this one. Heads or tails anyone?
So, there you have it. My opinion, with the disclaimer that, in spite of wasting far too much of my ever limited studying time, I didn't delve into the propositions as much as I could have.