Two considerations - is he a knut or not, and does he cut mostly vegetables, mostly meat, or a mix?
If he's not a knife nut, go with something in stainless, thicker stock - i.e. European style. There's no sense in having a thin, hard, Japanese style blade if it's going to be damaged with improper handling and then be difficult to sharpen back into useability.
Given a single knife for all-around use, the Chef's knife and longer blade will cover more tasks. However, a santoku would cover most of my kitchen work (which tends toward veggies and small cuts of meat, no huge roasts or whole fish to fillet) and be more generally useable. I can reach for a pointy boning or paring knife for the odd task that requires a point.
The best advice is to go to a store and find something that feels good in the hand.
Some recommendations:
European forged chef's knife - Mundial - not the fanciest, but a decent bargain
MAC - generally highly regarded
Commercial cutlery - thinner blades, plastic handles, will do lots of work for the price:
F. Dick Eurocut Line
Messermeister Four seasons
Japanese - Shun Wasabi - this is their stamped line, plastic handles, stainless. Good performance for the price, with thinner blade stock and harder edges
http://www.cooking.com/products/shprodli.asp?BrandNo=1441&DeptNo=5000&StyleNo=2509
Spyderco - basic santoku
I'm assuming that since your brother needs a recommendation, he probably doesn't have something super-fancy in mind. Most of the above recommendations skew to lower cost models.