I play $2/4$ Limit and occasionally $1/$2 No Limit. At my casino the custom is to tip the dealer $1 every time you win a hand and $2 if it's a really big pot. At the $2/$5 No Limit tables, a tip of $5 on each winning hand with a decent size pot is standard. In some casinos, dealers make more than minimum wage, in most they do not. Basically, in those casinos where they make little money per hour, their hourly wage just pays their taxes and their take home pay is made through their tips.
The obvious exception is if your table breaks the bad beat jackpot! Ours is currently at $166,000 and we almost hit it 6 times yesterday at my table. I was hoping to be able to tip the dealer REALLY big...but, alas, no such luck. When the bad beat has been broken before, when it was much smaller, the big winner has tipped $1000, the 2nd winner tipped $500, and every other player at the table tipped $100. If I would have hit the bad beat and been the big winner (whose hand was beaten), I was planning on tipping any amount above my 50% of the pot, which would have been slightly over $3000, leaving me a cool $80,000 to take home.