We used to be a Coldfusion development shop before hopping over to PHP in 2008, now we primarily develop custom Drupal websites.
I enjoyed going from CF to PHP, but I feel like I am getting a bit stale.
I have been looking at different things like Ruby, Python, Obj C (iPhone). The problem is, there just isn't enough time in the day to look at everything at once.
What would be a fun new thing to learn that would refresh me a bit and challenge myself to learn more?
Try interactive languages, you can test thing without the issues of compiling and setting environment variables, an example is python, ruby, javascript. Then search funny practices experiments and get fun, i learned a bit with these topics
Rather than attempting to learn a new language (with the necessary time that dictates), you could always read up on things that would benefit your current skill set (and could be worked on during working hours?) yet still broaden your horizons.
For example, do you make use of design patterns, unit testing, continuous integration, etc. with your current PHP development?
Why is there no time? You say you are interested in things like Objective-C and iPhone development, well then go do it. It all takes time and you can't be a master of every technology, so pick one and carve out a block of time, maybe 30 minutes a day, and work through it. I'm doing that right now with Cocoa and while the going is slow - at least compared to my day job - I'm making progress and having fun doing it.
From what you wrote, focus might be the problem here. I get that - I want to learn it all but the harsh reality is that you've got 168 hours in the week so choices have to be made. It depends on what your goals are. Want to whet your appetite for iPhone development? Think it would be cool to work with the SDK and make an iPhone app. Then I'd say give iPhone development a try and devote a little time every day for a month or two to it and see where it gets you. You won't be an expert, but you'll learn a lot. Grab the Stanford video podcasts on iPhone development and watch them. They are helpful.
There are open source projects out there all over the place written in a variety of languages. Most need help and you could benefit from that experience. Find one that looks interesting and dig in. There is some cool stuff going on in the open source world.
If you like UI development you might look into ExtJS. The Javascript skills that are necessary will apply for web development no matter what the server side languages is. I had several months experience with ExtJS when I tried this, but still it might be an interesting first exercise; and that is, I created an "Editable Grid" interface to crontab.
Do your custom sites support smartphones? That could be a fun area that also is useful for your business as some customers may want part of their site to be viewed from Blackberries or other smartphones.
Another thought is whether or not optimizing system performance appeals to you or not. This would include hardware changes but also changing various settings on servers as some software is notorious for having oodles of settings that one can try to optimize, though I'm thinking of IIS and Oracle to some extent here I'd think it could apply to other software, too.