There are a lot of great Android keyboards out there, from the gesture-based Swype to the button-enlarging ThickButtons mods, but if text prediction is your thing, look no further than SwiftKey, one of the best text predictors we've seen yet.
One of the high points of the stock Android keyboard has always been its text prediction engine, which, instead of just correcting words for you (like the iPhone does), allowed you to pick a word from a list of possible ones as you typed. It was pretty good, but the newly released beta version of SwiftKey brings it to a whole new level. It predicts your current word based on the one that came before it, and while it's not the first keyboard to do so it does seem to be the best — and it learns your typing habits over time, further increasing its accuracy.
The stock keyboard is pretty good at offering you predictions before you finish your word, but somehow SwiftKey seems to pick the right word faster. There are only three suggested words in it's list as you type, but that seems to be all you ever need, and it actually makes it easier to use. I don't know if I'll be giving up my beloved Swype for it right away, but if you prefer the more traditional touch typing keyboards, SwiftKey is definitely one to take a look at.
SwiftKey Beta is a free download, available in the Android market for devices running Android 1.5 and higher.