The checklist for whether items are in stock follows:
The products must be Visible in Catalog.
The products must be Enabled.
Product must have a stock Quantity.
The product must be set to In Stock.
If the product is set not to track stock, it still has to have a stock Quantity and be set to In Stock.
The product must be assigned to the target Category.
If using multi-website mode (or if you imported the products through Data Flow), the products must be assigned to the target Website.
You must refresh your Cache / Indexes, just to make sure.