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Me earlier:

"The most recent TI-89 has something like 3 megabytes of memory."

Alex wrote:
"Yes, this is one of those Celestaire things mentioned above. Weight 3 pounds."

 

According to the postal scale on my desk, the casio fx250 weighs four ounces while the TI-89 weighs eight ounces. If you throw in a manual and some accessories you might get a couple of pounds. If you want to look at one and check its size and weight in person, the TI-89 is widely available in office supply stores. It's very popular for calculus classes.

And:

"And I afraid that it consumes power like my stupid laptop"

 

Fortunately, no. It performs like a calculator. You do have to change the batteries once in a while, but they last for a very long time. The TI-89 also saves your work (many lines of calculation) when you turn it off. I turned mine on yesterday and found a little calculation on the screen that I had left there over six months ago. And the features are amazing. Check out www.ticalc.org for some good comparisons. 

 

These machines are not cheap, but there are plenty of lightly used ones available on ebay at reasonable prices.