Edge magazine is good for relatively impartial multi-format stuff was pretty much the workman's bible when I worked on the games department in my old job. It literally was required reading. However for more specific stuff you need to go solo on the format. X360 (think that's right name) tends to have either demos be they videos or playable and added stuff like achievement guides thrown in to them for the 360. OPM is about it when it comes to ps3 as for PC? Well PCGamer would be the best imho.