I've used Poker Strategy for the free $50, it is legit. You have to take a "course" and pass a "test" but it only takes about 60-90 minutes.

I received $50 the day after I passed the test. The money, like any poker bonus, must be cleared. I had 90 days to earn a ridiculous number of points (at Party Poker) in order to keep the money. However, any winnings above the $50 and any freeroll winnings you get to keep, even if you do not clear the bonus. At the end of my 90 days I was not even close to earning enough points, but I had built my $50 up to $125 and so even though I had to pay back the original 50 bucks, I had a 75 dollar bankroll when I was finished.

Be careful about accepting the $50 stake. Poker Strategy will forever be your affiliate, so you will never be able to get rakeback or other sign-up promotions from any site that you accept the stake on. Personally, I wish I had signed up to Party Poker using a forum that gets a $1,000 freeroll each month, which I think I would have ended up winning more than $50 in over time.