[spatulon]

Or turn it into a simple iterative process, instead of a recursive process. They explain how quite simply in SICP:

http://sarabander.github.io/sicp/html/1_002e2.xhtml (Ctrl-F "We can also formulate an iterative process for computing the Fibonacci numbers.")

Here's a Python implementation:

    def fib(n):
        a = 1
        b = 0
        i = 0
        while i < n:
            temp = a
            a += b
            b = temp
            i += 1
        return a

With that, fib(100000) takes half a second to compute on my machine.