In addition to increasing capacity, you should take the opportunity to review your backup policy and requirements.
Perhaps you should consider making CDs / DVDs of your photos (and then duplicate the disks and ideally keep one off-site). Possibly consider online storage.
You could look at your storage requirements in terms of - for example - portability, resilience, flexibility as well as pure capacity.
Do you need to share storage across more than one PC in your location - a Network attached solution might be appropriate.
Do you want to take your data with you - a portable external hard drive may be appropriate.
Do you want increased resilience - a RAID array (internal or NAS) may be worth considering.
Some thoughts to start with, anyway!
SD