Some of the problems are as simple as find the sum of all multiples of 3 or 5 less than 1000. There is one problem which asks u to find the pythagorean triplet a,b,c such that a+b+c=1000. There are also freakin big probs like find the last five digits before the trailing zeroes of factorial(1,000,000,000,000).

I just started coding for few problems. You too check those probs @ projecteuler.net