I think this is probably one of the more overlooked adjustments that a person can make..
Every poker site seems to have its niche as to what games are soft/tight. You may find that the softness/tightness of your current site doesn't fit well with your playing style, so a change can work out quite profitably.. Nevermind the insane amount of money you can make by bonus whoring at all of them..
From personal experience:
UltimateBet: Tight ring games, heard good things about the MTTs
Pokerstars: Tight ring games, soft SnGs, best MTTs
Partypoker: Loose ring games, soft SnGs (high vig on $5)
The Crypto skins: Between 4pm -> 9pm ET soft ring games after that it's a rock garden
Pacific Poker: Loose everything. If you can put up with a buggy client and very loose games at all limit, play here.
Prima: Can't really remember