selecting for type cast failures

Hi!

I am working on updating some of our tables to use appropriate native data types;  they were all defined as text when
theywere created years ago. 

What I am running into, though, is there are some records that have bad data in them, where they can't be successfully
convertedto int, or float, or boolean, for example.  

Is there a straightforward way to identify offending records?

I've been able to identify some with things like "...not similar to '(0|1)'..." for the boolean fields, and "...not
similarto '[0-9]{1,}'..." for int.  
Are regular expressions the best approach here or is there a better way?

Thoughts?

I've poked around on the internet and have found some people suggesting user-defined functions. I'd prefer to just use
aquery, since it's a one-time clean-up. 

(I'm using postgres 9.2)


Thanks!
Natalie