I am going to go against everyone here. I have been developing since the good old days of ASP and VBScript.
I tried, for some time CodeIgniter was pretty good, looked at CakePHP and used Symfony, which is pretty neat. I also spent some time with Ruby.
BUT I would say that stick with normal, good ol 'PHP (this, of course, depends on the size of your project). But for small jobs, pure PHP is great.
I highly recommend using the excellent HTML template system. H20 on GitHub is awesome. It is completely stolen from the Django project and allows you to create great HTML templates that can inherit basic templates. It is really simple, but eliminate the need for echo html lines. You basically pass the template to your variables. http://github.com/speedmax/h2o-php
Finally, the biggest recommendation I can make is to use a cool DB. Take a look at MongoDB, which is a document-based repository, but it will save you hours and hours by trying to save objects in a relational database when you can just save and retrieve complex objects from Mongo.
With all this in hand, I think you could build some really big, clean and serviced ones.
I am talking about this based on how difficult it is to return to a project like Cake, or CodeIgniter after 6-12 months, and how long I need to remember what happens and where everything is. I found it actually quite difficult to go back to Ruby on Rails, and CodeIgniter and finding a little neat PHP was always the easiest.
I also hate that when I have an update, tell Ruby + Rails how many things break and don't work. It can be much more painful than you need.
β’ So simplicity and elegance. β’ Easy to pick up in 6-12 months. β’ A small amount of code. β’ Intelligent database. β’ Easy for other people to use and debug. β’ PHP's bare bones must be fast and scalable.
Although PHP is still one of the most convenient languages, I find the syntax quite painful. And the lack of some convenience operators.
eg
$obj = {value1:"john", value2:"is cool", value3:[1,2,3]};
Personally, I think that it was a real pity that did not fall into a lot of debate.
Python in the Google App Engine is also a fantastic, great database and Django templates (hence my recommendations for H20 and Mongo DB).