Some useful info here:
EQUIPPED TO SURVIVE (tm) - Aviation Life Raft Reviews
This is perhaps more than you wanted to know, and is a bit dated (2000) but the price is right!
Also much other useful survival info at this site.
See also:
WINSLOW® Liferaft Company Home
Depending on how many persons involved, water temp, and and how far off shore you will be, you may want to consider:
http://www.switlik.com/pdf/isplr_brochure.pdf
or, Switlik helicopter crew and pax life vests:
Aviation Life Vests . After reading all the reviews, I purchased a set of the Switlik vests for my helo. I (thankfully) have no first hand user experience with these, but the quality appears very high and the Company was quite responsive. Vests may be a good idea in addition to a raft, as except for a near perfect entry into the water, it may be difficult to deploy and board a raft without personal flotation gear due to injuries, panic, etc, especially if some on board are marginal swimmers.
Keep in mind that survival times in colder water are very short, so flotation gear alone may not be enough. Additional info at:
Cold Water Survival. This is boating oriented, but once in the water, it doesnt matter so much how you got there!
Much additional info on the web; Google "cold water survival" etc.
Depending on where you are operating, you may also wish to have a portable satellite phone and/or some form of PLB/EPIRB. Unless float equipped, the acft will likely submerge quickly, rendering the ELT inop.
Dont mean to emphasize the downside, as the odds are very high that you will not need any survival gear; but if you do, being well prepared is the only way to go.