BA is a great resource (I really love the Handbook), and they've just released their top 100 prospects for 2009. You can find the list here.
We've got 4 Mariners in the top 100, but none in the top 50. Halman, Saunders, Triunfel, and Aumont all make the cut at 57, 65, 89, and 93 respectively. We have a pretty deep system full of high risk/reward guys but it's pretty lacking on good talent close to the majors, leading to a fairly low rank in the Handbook. Next year will tell whether we have a set of real prospects on our hands or not - Halman, Triunfel, and the SP trio of Aumont, Ramirez, and Pineda each have a lot to prove. We should also be able to add some impact players through June's draft, and it wouldn't be a huge shock to see our system turn into something special by this time next year.