If you like the ringtones that came with your device but they just aren't loud enough, check out
this post over at crackberry.com. It was in response to someone saying their ringtones were too loud, but everything in the post applies - adjust the volume to your liking. You can also apply this to your own custom ringtones.
I customized my Ringer_BBpro_4 with a gain of 105, and it seems good enough for me. I'm concerned that if I make it much louder I might damage the speaker.