If you want to have an sli config go for a full tower, you'll have more space and you'll need a motherboard with two 16x pci express slots. You could get a mid tower but you'd need to put some decent fans in it - if you by two non-reference gtx460 's (Gigabyte is good) you would be fine keeping them cool. The problem with non-reference cards is that they are near impossible to water cool with a full watercooling block as the screw placements differ from the reference cards.
Condensed version:
If you want to watercool your two gtx460s, get a full tower as you will have more space for the pipes, radiator, pump, reservoir etc.
If you are going to get 2 reference gtx460s, get a full tower as you can pack it full of fans to keep the cards cool.
If you are going to get 2 non-reference gtx460's, they will run cooler so you won't need as many case fans to cool them down, get a mid tower.
Having said this, some non-reference cards have very tall coolers on them, so if you did chose non-reference over reference, check how many pci slots they take up and make sure you will have enough pci slots for all of your hardware, graphics cards, wifi card etc. If you don't have enough, get a full tower, it will have more pci slots.
In terms of cases:
- The nzxt phantom is *very* plastic, so don't get if you think it looks cheap, but it does have a lot of space, it has good fan filters and a lot of space.
- Antec cases are very good at cooling.
- Fractal design focus less on good cooling and more on making your pc silent. Also inside the door, the front looks a bit cheap. Having said that, they are very classy cases, have good build quality and good dust filters.
- The corsair 400R can cream a coolermaster haf at temperatures - Corsair also have very good build quality and they really keep the temps down.
- The gelid darkforce isn't particularly popular, but it is a good case and more refined version of coolermaster's cm 690 II advanced. (it also has a nice window)
- The Nzxt switch 810 is very good all round full tower. It has good airflow, 10 fans!!
In a temp test (the temperature taken is the cpu temperature) it stays cooler on load than a corsair 600t, NZXT h2 and a corsair 650d.
http://www.overclockersclub.com/reviews/nzxt_switch810/5.htm This has some pretty good comparisons.
To chose the right case I would just go on a website like scan or ebuyer or newegg if you live in US and just read people's reviews to get a real insight into what the case is like from the people who own it.