It has been a while since I looked into these kinds of tools.
For example, the OST File Viewer – http://curah.microsoft.com/60115/use-ost-file-viewer-to-open-and-read-ost-files – is a simple and effictive tool to reading OST files where the Exchange server is offline or has been damaged.
To recover these types of data files, it is best to purchase a decent product. There are a number of products that handle a variety of files. Most will allow you to view the recoverable data before you purchase the product.
Another company, http://www.kerneldatarecovery.com/, provides numerous recovery and conversion tools.
If you are totally stuck with a failed Exchange server, Ontrack PowerControls http://www.ontrackdatarecovery.com.au/email-recovery-microsoft-exchange/, will be a very useful tool. However, it can be fairly expansive for a once off operation to recover a single mailbox.
StorageCraft’s Shadow Protect Granular Recovery for Exchange – http://www.storagecraft.com/products/shadowprotect-granular-recovery-exchange – is a great tool for easily recovering Exchange server mailboxes from ShadowProtect backups. Once great benefit is that you can license this on a project based 60 day version, which is quite inexpensive.