How to select a 2.4GHz chip antenna for a space-constrained environment?
Digikey has plenty to search through - I'm afraid you'll just have to use their parametric search to figure out what works best for you.  On a more general note, Texas Instruments has a nice guide for understanding some of the different antenna topologies that are out there:

http://www.ti.com/lit/an/swra161b/swra161b.pdf

If you can fit it, I really like the "Inverted-F" and they even provide the footprint to make layout easy.  The "Meandered Inverted-F" antenna might be a good bet for your application.