you can get the Phantom theme right off the blackberry site on your mobile browser. at least, you could a couple months ago.
I personally don't like it. I tried using right after I bought my phone before I put any extras on it and it slooooooowed it way down.
My fave application at the moment is:
nuTsie.com! Listen and Share your iTunes Music, Playlists, Songs, MP3s and CDs - nuTsie
If you have T-Mobile or AT&T it is awesome. syncs with your iTunes library and lets you listen to your music wirelessly. I have about 4000 songs in my library so this is a GREAT feature for the Pearl, especially since I can't bring myself to dish out the money to buy a microSD card larger than 512mb