Mario, Kirby, Soul Calibur, and Halo Dungeons are all the most worthy in my opinion -- they're some of the most recognizable titles out there. Plus, I'm familiar with at least one title of every series, so I could give pointers as to gameplay, techniques and so on. Beggars however cannot be choosers.
To all those who said Mario Dungeon, the only issue i have is this: What would they post? I mean sure there are mario games, but most mario games don't really need a walkthrough unless you want to go for that 100%. Another issue is that there are TONS of Mario sites.
In my opinion, I see Metroid as a perfect game for it. Not many Metroid sites. Maybe even a Xenoblade or Operation Rainfall dungeon. That seems pretty legit. Hopefully they make a Xenoblade sequel!