thesilentist just did a great job rounding up a collection of slim wallets on the market, covering everything from Brooks Brothers (relatively common) to Glenroyal (relatively hard to find).
Card-holder type wallets are great, their low-profile makes it easy to slip into the pockets of dress trousers without creating an unsightly bulge. In fact, I carry one everyday. For those looking for a slim wallet, I recommend Coach’s waterbuffalo moneyclip card holder, it has everything you will need: two single-card slots in the front and a larger multi-card slot in the center, plus a money clip at the back - enough room for four to five cards and some cash. The Coach’s card-holder is also pretty good value - price at around $40-$50; the leather quality is also decent, and will age with a nice patina over time. The only drawback? The single-layer leather is pretty pliable, cards with raised lettering (e.g. credit cards) will eventually leave an imprint if placed in the front-most slot.
For those looking for something more unique, I recommend one of these Goyard hand-painted card holders. The leather is double stacked alleviating the imprint issue that Coach card-holders have.