I have been fighting this battle ever since I left Blackberry.
I have tried almost everything on the market and only found one that I would recommend at this point - mostly because it is so customizable.
It is called "Ultra Keyboard" and can be found in the app market. It is relatively new, that's why a lot of people don't seem to know about it.
The best part about this app is that it will not only let you customize the regular and landscape keyboards, but it also has an option that simulates the SureType keyboard layout found on the Pearl, Storm, and a couple of other Blackberrys. I love the Suretype keyboard and though I have found several apps and hacks that simulate it, none have come close to the word prediction and user-friendliness as must as UltraKeyboard.
You will spend a ton of time customizing it (everything can be customized, from the colors to size of the keys), but once you figure it out, you'll never use anything else.
Good Luck.
ps - for the record, no, I do not work for them