Question: That has reg expression checks for phone, zip, email.
Comparison checks for email and password.
Bonus: masking and forcing letters and numbers only options.

I would like one that works well with this:
**<http://www.malsup.com/jquery/form/>**

This is a multistage sign-up and would work when step 1 is complete(the form) it would send it to the server (via url serialized) on valid success go to step 2, which is a sliding div system.

**What is the best way to do this, and combine it inside the above mention ajax form submit plugin's "beforeSubmit" option?**

Answer: 
You can try bValidator: <http://code.google.com/p/bvalidator/>
I like jQuery tools validator, it uses html 5 input types, support for server validation and a lot of other resources. <http://flowplayer.org/tools/demos/validator/index.html>