Welcome to Colorado! Since Fort Collins is more of a college town many rental terms coincide with the school year. You'll find that one year leases on houses start in June/July or August. This is the time you have the most variety and options to choose from. Properties are being leased now for the beginning of August, so students can secure their housing before they leave for summer break. There are always properties available though, as not all landlords run on this same schedule. The reply below gives you the top two sites and resources for rental properties in Fort Collins; http://www.NorthernColoradoRentals.com
If you have any questions regarding the differences between CA Real Estate and CO Real Estate don't hesitate to call. I'm a local Realtor, originally from CA, and have been here 7 years- so I am familiar with both areas.
Kindly, Carrie Holmes 970-988-0242