What is the best way to input text from an Android phone? Is there a decent spell checker available?

After seeing your comment under Otis, I may have an answer. I've never used any spell checker other that the stock but there is a feature within Samsung, and several other androids, called Swype. Basically, you place your finger on the first letter of the word you want and swipe over every letter in that word. It's quite fast once you get used to it and the keyboard will eventually learn which words you use most.