First you have a physical size limit of 9.5 mm in height and the 2.5" drive has to be able to support SATA II (3.0 Gp/s). OS-X can handle anything you can put into the system. You do want to make sure your firmware is up to date follow this Apple T/N on how to check & update EFI & SMC firmware updates for Intel-based Macs.
You have a few choices here:
- Seagate offers a 1.0 TB SSHD drive (HD & SSD as a cache)
- Toshiba (which is now in partnership with Seagate) offers both a 1.0 TB traditional & SSHD drive
- Western-Digital offers a traditional 1.0 TB drive
- Hitachi (which is now part of WD) offers a 1.5 TB drive.
Personally, I would go with a hybrid (SSHD) drive and not use the optical drive bay at all.
Why I recommend this is two fold: first you want to get the max out of your battery when your on the road with a dual drive setup expect 1/3 or more less time than what you're getting now. These 2nd gen. SSHD's are very good giving you the snap you want and yet not as painful as a SSD in the same size range in the pocket.