I subscribe to GamesTM - I've been buying it since issue 30something and it's great value for the amount of content - 180 pages an issue, the features are in-depth and mostly interesting, and the retro section is well done.
I buy the odd issue or two of Retro Gamer if the games covered interest me, and back before the Wii launched I used to buy Revolution magazine. It was great at the start - lots of content, nice price, and each issue came with two free mini magazines - one for DS coverage, and one for retro. Eventually though they scrapped the mini mags, then relaunched the magazine to appeal to kids, then finally cancelled it altogether. Sad considering how good it used to be at the start.
I subscribe to PC Gamer too, it's a good read now that they've increased the page count and finally, FINALLY got rid of the useless demo disc and focussed on providing DLC or free games via codes instead.
Since I got an iPad a few weeks ago I've been looking around for games magazines formatted for iPad too. Besides the iPad versions of Future/Imagine titles (which are just glorified PDFs as far as I know), there's a few designed specifically for the iPad:
PXL - Monthly, first issue free, then $1/69p an issue or $10/ÂŁ6.99 for a 12 month subscription
Atomix - Monthly, free
EGM Digital - Monthly (I think?), free
I just wish EGM would get a retina update!