Agreeing with other posters , i,ll add it also depends what your Camera settings are set at - eg; Small / Med / Large ?
If Quicktime is opening them by default , you can change that but what format are they from the Camera ?
I use Acdsee for all my Photos / Albums etc and do batch files for any Resizing to a specific size i require, but there are a vast amount you can try , or maybe something that came with your Camera Purchase.
As Britecguy said FastStone Products are fine and i use FastStone Photo Resizer occassionally and for customers PCs , it does the basic Resizing.
Overall it depends what Photos you have taken and what you will do with them , manipulate , print , or just store on Pc.
The more you play around with them - Crop / Rezise / etc , some loss will occur in those photos.