Fortunately for you, WoW Insider has prepared a simple makeover guide for your bank toon. If you've been treating your banker right, you've probably dressed them in the tuxedo sets made from Tailoring or obtained through the Noblegarden event. Complete the look with a perfectly matching pair of Frayed Shoes. You probably won't find these on the Auction House, but they drop from Level 1-5 mobs, so they shouldn't be a problem to farm. If you're too lazy (or unlucky), you can purchase Heavy Weave Shoes from clothiers in most cities. These also go very well with tuxedo sets but require Level 12. I personally keep my banker at Level 1 too keep her ego in check, so it's the Frayed Shoes for her.
Of course, the truly rich gift their bankers with a pair of Antique Silver Cufflinks, which can be obtained from the lucrative fishing daily quest. Non-anglers can troll the Auction Houses or trade channels for these beauties -- but be prepared to pay a steep price! These simple white items sell for over 11 Gold to vendors, so fishermen won't easily be parted with them. Some people marry their bankers or accountants to make sure the wealth stays within the family... so why not throw in The Rock and Gold Wedding Band to celebrate the influx of Gold? The Rock is an exorbitant gift you can purchase from vendors in Booty Bay, Silvermoon City, or the Exodar for a whopping 100 Gold. Gold Wedding Bands come from those Bags of Fishing Treasures, just like the cufflinks, and sell for 15 Gold to vendor so expect to pay similar if you don't fish.
Of course, if you're not into the whole wedding thing, there are a bunch of alternative rings for your banker to show off their bling. For the neck, you simply have to visit the ineffable Griftah and choose from his wide selection of wondrous accouterments. I would recommend Gritah's Talisman of True Treasure Tracking, available for a reasonable 8 Gold 75 Silver 35 Gold. It never hurts to have amulets that help you find more Gold, after all!
All bankers simply must have an off-hand frill. It's the latest trend in banker fashion. I highly recommend the Gothic and classy Bouquet of Black Roses which can be purchased from herbalism suppliers in Stormwind and Thunder Bluff for a hefty 50 Gold. A single Black Rose can be an equally classy statement, of course, but true connoisseurs know it's only a cheap 50 Silver from those same herb vendors. If you're more into celebrating your riches with a drink like those Dwarves, then might I recommend an Ornate Drinking Stein. This nice silver mug also comes from fishing and sells for 11 Gold to vendors, so players will likely sell it for around that price.
Finally -- and this is important -- no banker's outfit is complete without Mr. Peanut's exemplary eyepiece, the Noble's Monocle. Barring a top hat, the monocle is the ultimate finishing touch any rich banker needs to get the point across. Without a monocle, how can your banker exude class and show off wealth? Monocles are the epitome of high society (or evil geniuses...), so it's imperative that your banker sports one. Again, this comes from the fishing quest (why do you think those guys from Deadliest Catch bother?) and retails for about 11 Gold. Once you have most of these slots filled -- specially the monocle -- your banker should be all set to conquer (or at least enthrall) the financial world of Azeroth.