senthurbalan:
If I'm building a robot definitely I should keep a controlling board on the robot as well, what kind of board should I purchase if I'm building a remote controlled robot, how to program the board and integrate it in the toy ?
I know you said you didn't want to go for the "most basic model" - but I can assure you that if you are just starting out, that is -exactly- what you should do.
The most basic "standard" model of the Arduino today is the Arduino Uno, which uses the ATMega328 microcontroller:
You want to obtain one -exactly- like the one pictured, with a socketed DIP ATMega328 on it. Ideally, you should purchase this board from a reputable and legitimate supplier of official Arduino boards (if you are in the US - I'd recommend SparkFun or Adafruit); you will pay more going this route, but you will be assured of getting a first-rate product. There are cheaper methods to getting an Arduino, but unless you know what you are looking for, you will likely get a knockoff that is violating the copyrights of Arduino. That isn't to say you can't get a good quality Arduino clone that doesn't violate the Arduino copyright (there are plenty of them out there, some of them quite good) - just that you need to gain some experience (or do your research) before going this route.
One of the reasons I suggest this particular Uno for a beginner is the fact that you can easily change out the microcontroller if you need to (because you fried it or something - happens to all of us, not just beginners!); you can purchase "bare" ATMega328 chips (without a bootloader) - or pre-programmed chips (that have a bootloader on them) to replace your damaged chip if needed. The cost of the chip is much less than the cost of the entire board (think of the Arduino board as a "carrier board" with a simple programming interface and interface pins for the outside world, that the ATMega microcontroller is plugged into). In fact, when you get some experience, you can later take out the chip from the board, and put it in your own projects (known as a "standalone" setup here). You need only a few extra parts to do this.
There do exist alternative Arduino-compatible boards out there that use a different packaging of the chip to make the board lower cost, or to make it "lower profile" for shields or such; the problem with these boards for a beginner is that, since they typically use a surface-mount version of the chip - if you fry the chip or such, they are very difficult for a beginner to repair.
There are other Arduino-compatible boards out there as well that look nothing like an Arduino; they are designed to be as small as possible while retaining all of the functionality of a regular Arduino, and are more meant for easier "embedding" of the board into your projects, as well as prototyping (an example is the RBBB).
If you are willing to spend a bit more money, but have a much more rugged Arduino (so you don't blow the chip as easily) - the Ruggeduino might be something to look into; it is a clone Arduino, but designed to be more forgiving of beginner mistakes, as well as hold up to use in more demanding environments. The manufacturer of this bit of kit is a regular poster here on the board, too:
http://ruggedcircuits.com/html/ruggeduino.html
The chip isn't a DIP version of the microcontroller, but all of the extra protection circuitry means that replacement in the future isn't likely.
You should find that using a standard Arduino with the ATMega328 will easily meet your immediate needs and learning requirements, while still allowing you immense possibilities. Most of the time, when people think they have reached the limits of the Arduino, they really have reached a limit with their programming ability or knowledge about what is available to interface with the system. While there are practical limits on code and variable use on the Arduino that may mean you need to move to a better Arduino platform - or some other platform entirely - initially for learning (and many practical projects) they shouldn't be a concern.
Finally - with all of that said, and taking into account that you didn't want to use a "basic" version - there is the other "standard" Arduino - the Arduino Mega:
http://arduino.cc/en/Main/arduinoBoardMega
This Arduino offers a ton of possibilities - but again, it is much more expensive than an Uno, and if you damage the microcontroller on board, you likely -won't- be replacing it.
Finally - here is the list of all the "standard" Arduino boards (and "extras"):
...you may also be tempted by the Arduino Due; while it certainly seems to offer a lot of extra capabilities over any other standard Arduino, please recognize that this board is still in it's "infancy" as far as widespread adoption of use by the greater Arduino community members. Not many have played around with it, and those that have tend to remark on certain aspects of it which make it's use by a beginner fraught with problems (most notably the fact that it's outputs are only rated at a few milliamps of output current and a 3.3 volt logic system - which makes interfacing with certain TTL logic problematic unless you are experienced). Maybe in the future it will become more popular, but for now, I would not consider it "beginner friendly".
So, again, my recommendation for you is to start out with the Uno, and once you get more experience with it, you might want to move on to the Mega for larger projects. I'm sure that by the time you find yourself wanting or needing a better platform, you will have a better idea and confidence to ask the proper questions and do the right research to know what to choose for your needs.
Good luck, and I hope this helps! 