The most common 4" recessed LED lights in use today are the Cree CR4 or the Sylvania RT4.

The CR4 has better performance characteristics than the RT 4.
1. No noticeable delay when turning on
2. Better dimming performance.

The type and number of lights depends on the intended usage and the desired style.

Alternatively, you could put in CR14 troffers.

The following website has more details.
http://www.cree.com/lighting/products/indoor
You could also get an idea of the pricing from the link below.

Here is a link that might be useful: polar-ray

Thank you for the insightful information from all. Certainly enough to get me started.

One additional question: Using a 4 inch cans & trim, what should I counting as the "lit-up area" ? I remember that when I was using 3 inch GU10 50W, I was told count on 36 square inches of light covereage. Does 48" makes sense for 4 inch trims?

Thanks again! And keep the suggestions coming!

The 3" lights are more like little spots.

4' spacing is more typical, though the spacing may be reduced to increase the illumination.

After your help and some research, I have decided to go with Cooper Lighting RL560 "Halo". They are sold in both Home Depot and Lowes:

http://www.homedepot.com/p/Halo-6-in-White-LED-Recessed-Lighting-Trim-RL560WH-R-ONLINE/203561301#specifications

After taking 3 samples and temporary hooking them up, I like the 3000K light (83 CRI) that I am getting in my basement. It's also rated for damp or wet usage.

Before I go and buy about 25 of these, does anyone know or are aware of anything negative about this model?

Last, but not least: My future basement's open area is going to be 14 feet x 19 feet. The ceiling hight is just under 7 feet. With this in mind, I figured I will need to have 3 rows of 5 RL560's (spaced 4 feet apart) / divided into 2 zones. I will not be using dimmers.

Does it make sense?

If you can afford to wait, Cree has an expanded product range with color of 2700k, 3000k, 3500k and 5000k in the pipeline.

The halo lights aren't as efficient