Memory Leak...need help

Well, I've been working with Blitz for quite a while now and finally I caused a memory leak. Sadly, I created a large part of my game engine before I realised it was there. I added a counter to show me video memory usage, and as I expected the available memory drops like a rock as soon as the game fires up. At first it crashed me after a couple minutes, but now it just saps it down to five-six megs and gets really sluggish. I have no clue what could be responsible, so what I'm asking is, what is the best way to track down memory leaks? I've already checked for rampant entity creation...nothing there. Particles, projectiles, and effects rarely exist in the game for more than a second, and there is nothing else that I know of that could be a cause for this. How should I go about debugging this? Thanks in advance for any suggestions.