It's quite amazing how many different numbers we have here, all attempting to address the same question. Some are more or less correct, some not at all, and some are correct within the scope defined by the answer but not the question.
This confusion seems to stem from the fairly wide variety in the natures and origins of all the <PERSON>-type androids. In hopes of clearing this up, I'll try to cover this question from all angles.
All complete androids built by <PERSON>, and seen in Star Trek canon - Four
I'm starting here, with the narrowest category. This includes only the androids built by <PERSON> himself, which became fully functional, and are actually seen in Star Trek movies and TV series. This list includes the following:
* B-4
* Lore
* Data
* <PERSON> (AKA: <PERSON>)
All <PERSON>-like androids mentioned in Star Trek canon - Five
Slightly narrower in some ways, yet broader than others, this category is meant to cover all androids which Star Trek viewers would easily recognize as being "<PERSON>-like".
This category includes only androids which actually have similar design and programming as <PERSON>. These androids have a few specific features that make them unique from the others.
* They are physically modeled after <PERSON> himself. (Making them physically <PERSON>-like)
* If they are fully functional, they are programmatically <PERSON>-like if:
* They have their own identity which is fully pre-programmed.
* They are programmed to know that they are androids
This excludes <PERSON>, because she was not programmed to be aware of her true nature and her identity was not really her own. 837
Also, she looked nothing like Data.
This includes the prototypes prior to B4 because we can reasonably assume they were also physically modeled after <PERSON>, and the fact that they were not fully functional excludes them from the other requirements.
This excludes <PERSON>, because Data deliberately built her so that she could realize her identity, even including her species and gender appearance, on her own - it was not pre-programmed as with the others.
This list includes:
* Unnamed prototype #1
* Unnamed prototype #2
* B-4
* Lore
* Data
All <PERSON>-type androids mentioned in Star Trek canon - Seven
This is the most all-encompassing category of Soong-type androids. It covers all <PERSON>-type androids created by <PERSON> himself, which would include <PERSON> and all of his predecessors as well as <PERSON>. This also includes <PERSON>, who was later created by <PERSON>.
* Unnamed prototype #1
* Unnamed prototype #2
* B-4
* <PERSON>
* <PERSON>
* <PERSON> (AKA: <PERSON>)
* <PERSON>
All of the lists above are based on information taken from Memory Alpha. Aside from those already linked, there is another article which is important - TNG Season 7, Episode 10: Inheritance. It is important, because it is in this episode that we discover that there were three prototypes created prior to Lore. (If you want to review the episode, the pertinent discussion takes place around 20 minutes in.) These three are not explicitly named in any episode or movie, but they would presumably include B-4. This is why some of the above lists include two unnamed prototypes. Unfortunately, we never canonically find out much else about these prototypes other than that they existed. 837