How much money do you want to spend? I haven't checked them out recently but I think you can get a doubly suspended (both front and rear) for about $1K US.
What do you want it for? Riding around the city or hard core off-road riding?
It depends what do you want to do with the bike?
bike on the road?
On trails? paved or unpaved.
go on hilly areas?
Go overrocky areas?
youd be better off getting the basic kind of mountain bike and add on extras as needed for where you going to be and how your going to use your bike.
I was an active biker and hope to be again (if that's posible) and could help you if you want.
first off i ride all the time.i ride mountain bikes.i bought mine for 250.00.i`ve added a lot of extras on it.the most important thing is how does it take the hills.some bikes don`t take hills good others do.you should go to a bike shop and ask if you can test ride one.