Bitfinex & BTC-E are a good example, though you will have exchange hack risk (keeping money in an exchange sucks).
Anyways, say Bitfinex is 750, btce is 725.
buy the lower, sell the higher... Short (sell) Bitfinex 1 btc @ 750, go long (buy) BTC-E 1 btc @ 725.
When the gap comes near to closing, close both trades. (In Example, both Bitfinex & BTC-E are both priced at $742, close both trades).
Bitfinex trade = (1 btc * 750) - 742 = $-8.00
BTC-E trade = 742 - (1 btc * 725) = $+17.00
$+17.00 - $8.00 = $+9.00
You will lose on one trade, but win more on the other. It doesn't matter if btc rallies/falls $100s of dollars in the mean time, all you care about is the width of the gap between exchanges.
Eventually, one of your accounts will run low on funds (because it continually loses while the other side continually wins)... simply send bitcoin from the winning account to the losing account and balance their funds out... no FIAT involved... This to me seems to be the most straight forward way to arbitrage bitcoin in this day & age, granted it's a totally different concept than the one you have mentioned.
Also, triangular arb is another good idea, but bots have that one on lock, you won't find a single cent in profit from that one, trust me i've tried!!
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