Depends on where you are and your definitions of "small" and "light"-
I have a Hobie 14turbo and owned a Nacra 5.0 for 17 years. The Hobie is >100lbs. less than my 5.0 was and 2 foot smaller. For one person the 14 is great- not good for 2 (adult) people IMO while the 5.0 is good for one person (except racing- number sucks!) and great for two (IMO again). My Taipan 4.9 weighs less than my Turbo and is great for one or two but you could buy at least one of each turbo and 5.0 for price of a good 4.9. An Isotope 16 or Cheshire 14 are both light, small boats but unless you are in NC/SC area you won't see any- Mosquitos are great little boats and popular in Aus and South Africa but very rare in US. Lightest cats are "A" class cats- 165lbs. if 90's up- but they are definitely more of a "racing machine" and 18 feet long with 30' mast but only 7'6" wide. If you are new to cats I would recommend a good 14turbo or straight 14- if you learn to tack a 14 w/o jib (boat I learned on!) in any conditions you can tack any cat that can be tacked plus they are tough, fairly common, and relatively economical. Once you get good on it, and if you find you often get a chance to take crew out, you may want to "move up" to one of the other options.

Kirt