You would be very unlucky to get blacklisted in an RBL. There's a lot you can do to make sure your emails get through, the easiest and cheapest way is to get your users to add your sending address as a contact on gmail/hotmail/yahoo/whatever. Most spam filters won't put known contacts in your spam folder.
You can use something like
CleanMyMailbox - Whitelisting Instruction Generator to generate instructions for your users.
If you're sending a lot of mail/newsletters etc then you can look further into it, but as long as you're not sending off a shared IP/mail server then it should be ok.