The Duelist used to publish MTG puzzles by Mark Rosewater in which you were placed in the last turn of a game and had to figure out the correct play to win. I remember these puzzles being extremely fun and a great way to improve skills. I know that these puzzle were collected in Magic: the Puzzling, but with the M10 rules changes, these might be outdated/broken. Is there any other place I could find something similar?
ChannelFireball has a category mostly fed by LSV called What's The Play?, which features articles in sets of two, being a puzzle and LSV's respective solution that's realeased a few days later.
The puzzles aren't always win-or-lose situations, but also about what the correct play is to be best off for the rest of the match. The presented situations are mostly from actual game situations taking place, either from LSV himself, or by other players. You can also submit your own predicaments and have them featured on the format.
While LSV is handling the presentation, it's not intended as a "one person knows best" idea, but encourages people to brainstorm in the comments, where you can also see what other people thought was a good play, and why.
Since March 2017, there is a blog-style collection of puzzles called Possibility Storm.
As of now, the page is continuously updated Mondays, and features everything you need in a single image. All puzzles have a difficulty rating applied to them. Generally, the same blog post will have a solution hidden by default, although some of them are unfortunately only available after donating via Patreon.