The Best option of course would be keeping the game in Buffalo on New Years Day and building it up as an traditional event similar to the NFL's Cowboys playing at home every year on Thanksgiving. However my guess is that the NHL is reluctant to do this so this is a look on all the possibilities the league has.
The first issue is the when, and that is unlikely to change. The league planned well on scheduling the first game on new years day when television viewership is high. The simple fact that it is a day off of work for many people, and yet lacks the traditional and family activities of a day like Christmas is enough to give any television broadcast a boost. Given the NHL's driving desire for ratings success and the event's cry to be renamed the "ice bowl" it is not likely to be moved.
Where is a more difficult question. While their are thirty NHL teams as many either lack the passion for their NHL teams (Boston), are not in ideal climates for an outdoor game (Dallas), or lack a significantly large outdoor venue to make the event worth doing (Toronto). Here is a look at all stadiums capable of handling such an event.
Soldier Field (Chicago) - With a capacity of 61,500 it is large enough to hold the event, and snow would be no problem in Chicago either. The downside is that the team is hardly able to sell out it's home games in a much lower capacity arena. The other side is that Kane and Towes are both very good and that hockey will be regaining popularity in Chicago, and that the franchise doesn't look much different then the Sabres did five years ago.
TCF Bank Stadium (Minneapolis, Minnesota) - As far as outdoor venues go it is slightly on the small side with seating for only 50,000 but would sell out with no problem in hockey mad Minnesota. The NHL won't push this though as currently the Wild lack the star power that the Sabres and Penguins have, but if the team keeps making the playoffs every year that could change.
Ohio Stadium (Columbus, Ohio) - One of the largest venues in the Northeast it is not an ideal location for the game at all. While Ohio has enough fans to support the Blue Jackets, they don't have many more and an outdoor game would be unlikely to attract more than 40,000 or so, not even filling up half the capacity of the stadium. Additionally given the success of the Ohio State football program, fans in the area may be slightly more interested in the bowl games.
McMahon Stadium (Calgary) - While Calgary can easily get behind hockey, the question is to the stadium's size. Naturally the stadium only seats 35,650 which is hardly impressive. That said the stadium is capable of accommodating temporary seating. If capacity can be brought up to the sixty to seventy thousand range then it could work, otherwise it just wouldn't be worth it.
Invesco Field at Mile High (Denver) - One of the few American markets capable of supporting the game Denver wouldn't be ideal but could pull the event off. The popularity of the team has fallen slightly in Colorado, but that probably has more to do with the success of the Rockies then any decline in the popularity of hockey. The other problem is Denver is not near any other NHL cities so the ability to draw many fans from the away team is slim.
Lincoln Financial Field (Philadelphia) - The Flyers have improved enough since last year that pulling off this event isn't too unreasonable. Within driving distance of New Jersey, New York, Pittsburgh, and Washington the game would have no trouble selling out.
Heinz Field (Pittsburgh) - An obvious place to hold the game this was actually the NHL's first choice for the Winter Classic, but was moved after ownership indicated that they were more willing to be the away team. Unlike the Bills, the Steelers actually could get a home game in the playoffs, so a match up would be dependent upon NFL scheduling.
Gillette Stadium (Foxborough, Massachusetts) - Hockey is big in Boston with an original six team, and a thriving college scene as well. However in an assessment I agree with The Boston Globe notes that this is unlikely.
Giants Stadium (East Rutherford, New Jersey) - The Devils are not by far one of the larger draws in the league, but a game against a New York opponent such as the Rangers would guarantee a sell out. That said complications arise from the fact that both the Jets and the Giants share the facility, and finding a ten to fourteen day block to set up the rink would be near impossible.
Olympic Stadium (Montreal) - This one could happen. Selling hockey is not a problem in Canada, and furthermore the Canadians are celebrating their 100th year as a hockey team next season. However the Stadium itself has a few problems. Currently the Stadium has a roof prevent it from being a true outdoor game. However the fire martial has forced the venue to close during the winter due to problems with the roof, and now that the Expos are gone the roof theoretically could be removed. The complexity of this facility may not make the game worth it.
Commonwealth Stadium (Edmonton) - Was the home of the Heritage Classic, and could host an outdoor game again. Edmonton is a small town, but hockey is big there, and a game against the Flames would be even bigger.
Ralph Wilson Stadium (Buffalo) - Just hosted the event two days ago, and is more than ready to host it again. The city of Buffalo and the fans of the Sabres are all behind maintaining the event. The question comes if the NHL is committed to moving the game elsewhere, and Buffalo is committed to hosting an event like this again. The league may or may not be willing to have two outdoor games in the same season, but it may be something that will happen. Buffalo has enjoyed the success of the first game and is up to see it happen again next year.
Toronto - Probably the biggest hockey city in the world Toronto lacks an appropriate venue to do this. BMO field is much to small, and the Sky Dome (or whatever they are calling it nowadays) is barely outdoors, let alone a really odd configuration for hosting a hockey game.
Beaver Stadium (State College, Pennsylvania) - Rumors about the Flyers wanting to host the Penguins here have been swirling. While not in either city, it is close enough to both of them and significantly larger than Heinz Field or Lincoln Financial Field. Given the league's love affair with Sidney Crosby this could happen. However like with Ohio State, when you hold the game in the stadium of a successful college football game, the worry that local attention may be elsewhere. Of course if the league takes the two game approach, the Sabres could have their game on New Years, while this game could be played later in the season.
Ford Field (Detroit) - While not outside, there has also been talk about the Red Wings playing in the final game of a triple header at Ford Field following two college games. While this would allow for more seating for the Red Wings the attention would most likely be more on the college clubs than anything else.
Another option that the NHL has is to make it a Penguins, Sabres classic with both teams in the game every year, and the event alternating cities. While this leaves out the rest of the league, it may be a nice compromise between those who want to keep the game in Buffalo, and those who want every televised game to feature Sidney Crosby.