1967-68 to 1969-70: Philadelphia, Pittsburgh, Los Angeles, Oakland, St. Louis, Minnesota
The six new teams added to the league in 1967-68 were so awful they needed their own division to protect them from the rest of the league. The expansion teams played each other ten times in the first expansion season (four vs the original six), eight times in the second and third (vs six), and finally moved to a balanced schedule in 1970-71 and stayed there for four seasons (after adding Chicago and Atlanta), making the notion of divisions fairly irrelevant. But in the first season in particular, the travel was ridiculous.
1974-75 to 1975-76: Houston, San Diego, Minnesota, Phoenix, Michigan/Baltimore then Denver/Ottawa (WHA)
The WHA had a Canadian division and what amounted to a Mid-West division, but needed to funnel the rest of the teams into their own division. The "West" division, as it was known, was spread out and became more so when the Detroit-based Michigan Stags folded and moved to Baltimore late in the season. The league doubled-down on this division in 1975-76, putting a team in Denver. Denver moved to Ottawa while the team was on a road trip (!) and Minnesota folded later on in the season.
1974-75 to 1980-81: Montreal, Los Angeles, Pittsburgh, Washington (later Hartford), Detroit
1974-75 to 1975-76: Oakland, Boston, Buffalo, Toronto (1974-75 and 1975-76 only)
The NHL re-aligned in 1974-75 and started an unbalanced schedule again. And by unbalanced, I mean nonsensical. With only three teams in the West (Vancouver, Oakland and Los Angeles), they couldn't create a logical Western Division and instead put those teams in with teams that were nowhere near them. I can't decide whether the Kings or the Seals had the best division, but today, I'd be leaning towards having the Habs, Wings, Pens, Caps and Kings together. Oakland and Kansas City both moved in 1976, which again prevented the NHL from having a Western division.
The Atlanta Flames folded and like the second time Atlanta lost a franchise, the NHL didn't bother changing the schedule. Calgary, LA and Minnesota played almost all of their games on the East Coast; Chicago spent most of the season in the West.
In 1981-82, the league re-aligned logically, and in 1982-83, moved Winnipeg and New Jersey into the divisions they'd reside in for over a decade. Until the current season, there was no team movement and there were no major expansions.
2011-12: Washington, Carolina, Tampa, Florida, Winnipeg
Winnipeg in with its natural rivals!
Future: Toronto, Montreal, Ottawa, Boston, Buffalo, Florida, Tampa
I suppose you have to put the Florida teams somewhere, but this division is justified only by the assumption that elderly Floridians are primarily Habs and Leafs fans. Once Florida relocates, we'll no doubt see another realignment.