With the whole MySQL/Oracle issue going on, I find myself looking into the future and how I see it. As far as I'm concerned, MySQL will start to lose it's popularity as the landscape changes. As far as I am concerned, there will be two key players in the MySQL replacement market, those being Drizzle and MariaDB.
I am not just saying Drizzle just because I help out with the project in various ways, however, that should be a good sign that I believe in it if I am willing to put any effort into it. With people behind it like Brian Aker, Eric Day, Monty Taylor, Stewart Smith, Jay Pipes, you've got a coding powerhouse that could solve the cancer issue if it was up to software development to fix it. These guys work around the clock and have been refactoring and re-examining everything inside of MySQL. What's going to be left ideally is a superfast microkernel that supports plugins for everything - leveraging the best options out there for replication, messaging, storage engines, etc. Growing apart from the monolithic huge distribution model that MySQL currently follows.
The second key player is MariaDB. Another fork off of MySQL, led by Monty Widenius himself and with other MySQL key players behind it, there is no doubt it will continue Monty's legacy as being able to spin success out of a tiny little open source product. I believe it will stay more traditional in-line with MySQL, but will provide more advanced functionality and scalability as it is developed further.
I won't get into other options like PostgreSQL as I don't follow the rest of the community there much.
Also, we'll see more NoSQL (did we ever bottom out on a better term for that?) options. CouchDB and MongoDB (both of which from a 50,000 foot view look identical from a usage model) and options like Cassandra will also become important and your data needs will become the decision maker for going with a SQL or a NoSQL database. Both of which offer advantages. However, I see Drizzle as making huge strides in leveling the playing field (or attempting to) with it's replication work to make it as scalable as NoSQL databases seem to be with their ability to scale out and replicate changes easily (which to me are their main selling point right now...)
Anyway, this is from a user perspective, not a developer perspective, and from what I've seen from #drizzle on freenode, a few SQL and open source conferences, blog talk and my own gut feelings.
I should make a note that I still use MySQL and will probably continue for some time. Neither Drizzle nor MariaDB are production-friendly yet. However, I believe 2010 should see the first "production capable" release of Drizzle (not sure of MariaDB.)
It is an exciting time though as we're starting to be presented with more options by the day, in fact there are so many various NoSQL databases now, key/value stores, and even a few more SQL databases that it's too hard to keep track of them anymore. There's a lot of code being written and with this whole Oracle possibly inheriting MySQL depending on the EU's judgement, it could ultimately help usher in some of these smaller projects into the spotlight quicker depending on what Oracle does with MySQL...