Is kabbalah the one and only form (source?) of Jewish mysticism?
From the first 60 seconds of this shiurby Rabbi Alan Brill it is clear that there are other types of Jewish mysticism outside of Kabbalah. The wikipedia list cited in another answer does not clearly make this distinction. Texts such as the the Sefer Yetzeirah or the Heichalot literature differ radically in their form of mystical expression and understanding, as does the mysticism of Rabbi Avraham ben HaRambam cited in another answer. From the academic perspective the main text of the Kabbalah is the Zohar which is believed to have been written by Rabbi Moshe DeLeon in the 1200's, as such there are several mystical works which predate it. For a good summary and overview see the introduction to "The Early Kabblah" by Yosef Dan. Rabbi Aryeh Kaplan presents the orthodox view, which is the information in the Zohar has existed from a much earlier period and was passed down orally until Rabbi DeLeon published it.
Whatever the case may be unless you use kabbalah in a colloquial sense to actually mean mysticism (which I understand from the question is not the case) the works cited above are representative of different schools of orthodox Jewish mysticism that are separate and apart from Kabbalah.
'Kabbalah' means "received", i.e. received knowledge. It is an oral tradtion, but has been recorded in several books. Many consider it the 3rd pillar of Jewish knowledge (with the Written and Oral Torah being the other two). So you can't really have another form of it - that would be a contradiction of definition.
The Zohar (meaning brilliant/radiant) is the most famous book, and is what most people mean when they say Kabbalah. So perhaps that is what you are asking. And if you are, the answer is yes, there are other books too: Sefer Yetzirah is the most famous (and oldest) of them. The Etz Chayim from the Ari is another.
Chassidut is inwardly based upon the ancient doctrinal tradition of Kabbalah. Outwardly it gives new emphasis to the simple and joyful service of God, particularly through prayer and acts of loving-kindness. In Chassidic thought, the abstract and often impenetrable formulae of classical Kabbalah are recast into the psychological terms of human experience. (from inner.org by Rabbi Yitzchok Ginsburgh)
Wikipedia has a list of some others that I have not heard of till now.
There was a a kind of religious path that developed around the 1200s which was close to the Sufi path within Islam. A major book in this stream was written by Avraham the son of the Rambam. It was re-published recently by Feldheim with an English translation as The Guide to Serving God. There are also a couple of Hebrew translations that have been published recently (the original is in Arabic), so maybe the ideas are undergoing a bit of a revival at the moment.