I was wondering what the correct version of this sentence is
私{わたし}が木{き}好{す}きです。 私{わたし}は木{き}好{す}きです。
If the correct version is even there.
は is generally used in the sentence with adjective like 彼女は美しい、海は広い. So 私は木が好きです is general.
However when it is the answer for a question and you identify the person, が is used. For example, "誰が学校で一番美しいですか?""彼女が一番美しいです". So if you identify the person who likes trees is you, you say 私が木が好きです. http://www.alc.co.jp/jpn/article/faq/03/19.html
In addition, you can place が and は after 木, if you use が, it has normal meaning, but if you use は, you can imply contrast or emphasis like you especially like trees. However I feel 私が木は好きです is unnatural.
bcloutier’s answer makes a dangerous shortcut! The truth is that は marks the topic, not the subject, and が marks the subject, not the object.
Often, the topic and subject coincide, but in this case they’re different. 好き just means “favourable, enjoyable”. It’s closer to an adjective than a verb (though the two concepts blur together a little in Japanese). If something is 好き for you, that means you like it. It’s not a transitive verb like English’s “to like”. And the absolutely 100% literal translation of the correct sentence, 「私は木が好きです」, is something like “(Topic: me.) Trees are favourable.” In other words:
Now, in this specific case, from an English angle, the topic is very subject-y, and the subject is very object-y. But it’s dangerous to look at it that way, because it’s vague, and hides what is really going on.
It should be 私は木が好きです。は comes first because it defines 私 as the subject. Since 木 is the object, it gets が after it. 木は私が好きです would mean "the tree likes me".