I am a PHP developer from last 2 years. I have worked into db stock systems, support systems sending mails and receiving mail scripts etc.
Now i have a good knowledge of PHP,MYsql,HTML, CSS now. But untill now i have worked in a syntax highlighting editor.
My question is "What I must learn next in order to further improve or diversify my php skills"?
Other thing, because being with webhosting company, I have never worked on any ecommerce site, so have no idea of shopping cart or payment processing or implementation of e-commerce site. So in this regard, what things/tools/technologies are necessary and are their any guides which can help me learn building the e-commerce websites? including all, the shopping carts as well as payment processing.

for payment processing learn for php security like ssl etc.. Also learn PHP OOP and read Advanced PHP book.

I'd say learn Javascript, purely because of how pervasive it is, the vast majority of sites designed in the last two years are thick with Javascript. Even if you intend to stick mostly to lower level work, knowing Javascript well, and knowing a framework such as JQuery well, will help you enormously.
The other key is to abstract away from the language, if you don't already use design patterns, get a good book on them (preferably not a language specific one).
For the ecommerce side of things, research external payment handling companies, PayPal integration, Google Checkout and so forth as well as reading up on best practices for secure data transfer (SSL, hashing, PPK cryptography).

I'd agree that learning javascript would be worthwhile, mainly because AJAX is becoming so common. It would also be worth learning a little about XML, REST and JSON. Are you aware of the free zend framework (http://framework.zend.com) ? That would probably be worth reading also.

I'd agree Javascript too, you will find it easy to pick up the basics with your existing knowledge in PHP etc.
Javascript will allow you to improve the website GUI etc. Don't go over the top though, remember not to start throwing in AJAX everywhere too - only use where you can make a real improvement!
Now i have a good knowledge of PHP,MYsql,HTML, CSS now. But untill now i have worked in a syntax highlighting editor.
I'm not sure what you mean regarding the syntax highlighting editor, you mention it as if it's a bad thing! Syntax highlighting editors are a wonder and it can become difficult using a plain editor with no highlighting.

Javascript, Ajax, C

A framework like Code Igniter would be a good thing - plus a modern js lib like JQuery.
For ecommerce specific issues - read tutorials about security and study some free open source scripts like oscommerce, zencart, prestashop etc.

There is a number of PHP Frameworks out there - consider taking a look at each and chances are it will simplify your tasks.
As of E-commerce, you could probably request API documentation from the most popular payment processors (Authorize.net, PayPal, 2Checkout...) and try to implement a sample solution using them. You'll most likely encounter SSL, Blowfish, GD library and other cool stuff :)

IMO the best thing to do when learning any programming language is to familiarise yourself with any common mistakes people make, and exploits that are used, it'll save you a lot of time in the future :) I'd also recommend javascript, I've not learnt much of it yet but it's greatly improved the functionality of the applications I've made.

I am a PHP developer from last 2 years.
My question is "What I must learn next in order to further improve or diversify my php skills"?
I think an important question is "what are you trying to accomplish?"
Start your own business? Go free-lance? Get a promotion?
There are lifetimes of skills to learn out there, i guess you need to specialize.
I couldn't recommend anything in particular until your goals are clear.
Lawrence

I think an important question is "what are you trying to accomplish?"
Start your own business? Go free-lance? Get a promotion?
There are lifetimes of skills to learn out there, i guess you need to specialize.
I couldn't recommend anything in particular until your goals are clear.
Lawrence
I whole heartedly concur.
There are a million different directions you can take as a PHP Developer. If you're working with a lot of database oriented material that lacks data manipulation or regurgitating information for multiple requests, you might want to step a little away from PHP and look into other *software* like memcached. On the other hand, if you're working on highly interactive websites and deal with a lot of aesthetics, AJAX and JavaScript are probably good choices. Alternatively, you may need a back end to handle special tasks or requests that may not come exclusively from the HTTPd so learning a language like Java might come in handy.
This is a route that only you can determine. Look at where you want to be a year from now, and forecast what you will need to succeed. If what you are doing right now doesn't require you to learn another language, why not focus on how to secure your code a little more? Or optimize it to be more efficient by writing a benchmarking script and changing things until you've perfected it.
You are the captain of your own ship :).

What maknet said..
Personally I expand my knowledge/skills based on mine and my client's needs. You mentioned ecommerce, but why? Is it something you need, or just would like to expand yourself to?
Do you have a specific goal, or are you just trying to become an overall well rounded developer?

Besides AJAX, JSON, XML, OOP in PHP (very useful) and javascript frameworks you might find it useful to learn how to use other languages with php. For example, have you ever considered using C or Java in addition to php server side? When it comes to processing large complex data sets, PHP has its practical limits. Have you ever messed around with PHP optimization software?

What maknet said..
Personally I expand my knowledge/skills based on mine and my client's needs.
Same here. Or at least my employees get to expand their knowledge depending on client requirements.
I mean, if you're going for "buzz" knowing e-commerce may not be the way to go for your resume. Something like AJAX is new and buzz-worthy and isn't as technical as "I know a PHP CMS" or else the interviewer conversation might go like:
"I know PHP CMS's like Drupal and Wordpress"
"uh, ok.. but do you FLASH?"
"Yes, i can do action-script"
and the interviewer looks at the checklist, and says, "Is that like Flash Action-script"?
and you're like, "Maybe i don't need this job..." :)
Lawrence