I think you may have two options. The first is to try iMobileMail (http://www.imobilemail.com/)
. I use it and I think it would work well for the purpose you want. However, it costs $23/year, and it doesn't store the e-mail on the device, so you must wait for it to download all the e-mail from the account whenever you want to check.
The second option is LogicMail for Blackberry. I've never used it, but there have been a couple of recent posts about it here LogicMail - POP/IMAP checker! (free, open source, OTA install)