asp.net developer - new to the OS scene - need advice

[eluser]Sgt Quagmire[/eluser]
I have been developing and designing web apps for 3 years now (professionally) with asp.net. Now that I have graduated college I am interested in doing some sidework.

My dilemma is trying to figure out the best route to take with open source technology. I have went through a few CI tutorials, and I must say CI is a very intuitive framework and actually fun to program with. I just don't know whether or not it is the best route to go for making web sites quickly.

What I'm looking for is the best, and quickest, way to develop a site that has a blog, login/register, and forum. Along with these I want to have to option to develop or add existing modules/plugins if the client needs it. Some examples would be using the twitter api, a simple cms, data management, and jquery widgets.

I've been googling and researching this stuff for weeks now, and still haven't managed to decide on which technology to invest my time learning. I work full time so time-saving is definitely a priority. My true expertise are with html, css, and jquery. I also know C# and have a solid foundation on OOP and MSSQL. This is why I have also looked into Kohana, but the community, documentation, and existing code samples have no comparison to CI.

If anyone here could give me some insight I would be grateful. Codeignitor? Kohana? Joomla? ModX? I have no idea lol...