I ended up buying the 2 Dark Avengers books today (haven't read them yet). I'm really only reading them because I'm looking forward to the Bullseye: Hawkeye mini series in April.
I'm vaguely interested in Iron Fist, but more so Moon Knight. There's a tpb covering 1 - 25?! That seems pretty intense.
Yeah right now would be the ideal time to get into Moony because of the new arc that started at 26 like Crono said. This is the 5th storyline so far in the run since the reboot. Luckily you didn't miss out on much because they've all been really slow moving stories, but you might be confused by Spector's relationships; but nothing too bad. The first one and the previous one so far have been the the most interesting so far with this one already shaping up to be just as good in only 2 issues.
Just as a side note on MK, if you really want a great self contained read, pick up #13. It's just how Marc passed his registration exam, which was hilarious, and even gives you a little idea why he goes by the name Jake Lockley now. Artistically its the most memorable book in the whole run, and that's saying something given that David Finch did the art on the first 8 issues and his pencils are probably some of the best I've ever seen.
As for Iron Fist, can't really be much help to you there. I bought the first 7 when it started but I fell behind and never went back to catch up. They were good, but too much came out at that time and it just got lost in the shuffle for me.
Sheep Cannon: (noun) A cannon discreetly disguised as a harmless sheep.
Usage: See issue Deadpool #16: Assignment in Greece
I hate you Grant Morrison, your package, and everything about you.