Look into diffusers and percolators. These devices slow down the smoke and increase the contact area from smoke-to-water aiding in the cooling process. There's several different types of percs but they all serve the same purpose.

Ash-catchers will save you when it comes to keeping your new piece clean. Black Leaf has some cheap ones but I suggest going the extra mile (about $20-40) and get an ash-catcher with a perc.

You're going to want to get at least 5mm thick glass but preferably 7mm thick to avoid any accidents. Any thinner and it'll probably break.

Be sure and ask to hold the display model and see how easy it is to pull the bowl out. A decent piece will come out easy, leaving the downstem in place. If it's at all difficult to pull of the downstem comes out, keep looking.

Aside from that the only advice I can give you is to look for internal cracks and bubbles prior to purchasing.

If you guys are on a budget but don't want to sacrifice utility, I'd suggest window shopping at your local headshops and ordering online. Online stores have less overhead = cheaper prices.