What are you looking to spend? Do you want Auto everything or are you ok with manual everything? Those are a couple conciderations as to what is the lens for you.
My tank isn't very large so I don't need to be able to focus on objects further away with a macro lens so I use a 55mm f2.8 micro-nikkor AI-S I picked up on ebay for a decent price. Great lens, due to compatibility (have a D90 so the metering doesn't function) I have to use it as a manual lens only, which is not a problem. I am saving my pennies to get a 200mm f4 AI-S micro-nikkor though. They can be grabbed on ebay for about $400-450. vs $1k-$2k for the AF-S version. I have been using Nikon for years though so I stick with what I am used to and what I like.
The biggest thing you need to figure out is what do you want to or can you spend.
there is a sticky at the top of the forum that may help you out as well.
Cheers!