Well, the Unrated Extended version is just that. It has about 10-12 minutes tacked onto it, and it really adds to the story between Kraven and Erika. It also explains Michael's backstory, and fills in parts of Selene and Michael's relationship. Little more action as well, just alot of it was originally cut for pacing.
There's also A TON of extras on the 2nd disc. Behind the scenes, interviews, costume designs, TV specials, etc. The audio commentary with Scott Speedman, Kate Beckinsale, and Len Wiseman is awesome. Very funny, and informative.
I bought it, and love it, personally. But, you may be better off finding it used if you do want it, because $25 is a little steep for this one.