This yeast is famous for its clean flavors, balance and ability to be used in almost any style ale. It accentuates the hop flavors and is extremely versatile.
Optimum Fermentation Temperature: 68-73 °F
Alcohol Tolerance: High
I've used this yeast myself. Its a good yeast, clean, with good attenuation. There are a TON of good reviews on it on White Labs website itself, where, I shamelessly ganked the above statistics.
From Northern California. This strain is more fruity than WLP001, and slightly more flocculent. Attenuation is lower, resulting in a fuller bodied beer than with WLP001.
Flocculation: Medium to High
Optimum Fermentation Temperature: 66-70°F
Alcohol Tolerance: Medium-High
I haven't used WLP051 myself, so I can't comment. There are a bunch of user reviews of it and its characteristics on White Lab's site.
I don't know what happened to California Ale II, III, and IV, but it's possible that those are pro-grade or brewery specific yeasts that White Labs are not allowed to sell to the general public. They may also be so close to California I or California V that it doesn't make sense to release them. They may also be elements of another yeast I have listed below. It may be a good choice for you as well.
WLP060 American Ale Yeast Blend
Our most popular yeast strain is WLP001, California Ale Yeast. This blend celebrates the strengths of California- clean, neutral fermentation, versatile usage, and adds two other strains that belong to the same 'clean/neutral' flavor category. The additional strains create complexity to the finished beer. This blend tastes more lager like than WLP001. Hop flavors and bitterness are accentuated, but not to the extreme of California. Slight sulfur will be produced during fermentation.
Optimum Fermentation Temperature: 68-72°F
Alcohol Tolerance: Medium High
Reviews for this yeast.
Apologies to White Labs again for shamelessly ganking information from their web site. Anything in italics is theirs.