First of all pardon my English. I am not a native English speaker

I have been a Web Developer for the past 4 years. In these 4 years I have spent my time on the internet to learn things. My current skillset comprises of

1. HTML
2. CSS
3. PHP
4. MySQL
5. jQuery (I would not say js and rather say jQuery because I am good at using jQuery and bad with plain javascript.)

The above things seemed like an easier part of my life as I quickly learned them. But now I would really like to enhance my skillset and I am pretty confused which way to move ahead considering that I have to learn things using the web and references on my own.

Design

My first option is towards design. Shall I get started with design and start using Adobe Illustrator, Photoshop, Flash, Flex. Designing along with my previous skills looks like a money maker to me. As both are co-related to each other when web design is considered. And its easier to learn the first 2 and I hope I can get tutorials for the last 2 as well.

Marketing

A lot of my existing clients asked me if I do SEO. So this looked as a good field to me as well. I cannot estimate the scope of SEO but I assume it has a long future. Since I am business minded as well and there are a lot of tutorials around, should I start with SEO, SEM, Social Media, PPC or whatever it consists of.

Software Development

The complex plight and hardest thing (perhaps) but the easiest way to find a decent job in my location. If I go for software development what platform should be that I should be ideally going after? Should it be C# for windows development, or ASP.NET (once again enhances my skill set), J2EE (there are a lot of jobs for J2EE developers here) or plain C and C++.

Also I think it is difficult to learn software languages right from Hello World, using internet? I have no clue how I learned PHP but I am sort of a pro now, but these other languages seems like a disaster to me? I cant figure out the reason if its because PHP is easier or there was a lot of tutorials around for PHP.

Anyways is it also possible to learn software development right from Hello World using the web?

Database / Server (Linux) / Network Administration

Seems like a job with a decent pay but less number of jobs and a bit harder to learn online. (not sure)

What should be the right track I should move ahead.

P.S - Age is not a constraint for me as I am between 20-21, and I come from an IT background.

I know quite little basics about

1. C (upto structures)
2. C++ (upto objects, I was not able to understand templates)
3. Core Java (some basics and OOP concept)
4. RDBMS
5. Visual Basic 6 (used to do this long back)
6. UNIX (a bunch of commands like who, finger, chmod, ls and a bit of #bash)

Or is there anything else that I left out?

I need you guys to please give me a feedback and the reason why I should select that field.