On the PC get Silent Storm which is a WW2 rip off of xcom/jagged alliance etc action point based. IMO the use of cover actually makes the battles better than XCOM though there is none of the base building/research side. A warning though: the battles can last for hours.
Fire Emblem on the GBA/DS is very good and the only non XCom style turn based game I'll be recommending today! It's Advance Wars crossed with an RPG. You keep all your units from one map to the next and they gain experience and level up from kills.
There's a newish PC game called UFO Extraterrestrials that got pretty slated in the press but with all the user mods (which are now available in one mod pack called BMan's) it plays as a good remake of xcom.
Finally there's an open source UFO remake that I can't give much opinion on cause I haven't tried it in years: http://ufoai.sourceforge.net/
There are rumours the Bioshock guy is working on an XCom remake and if he is hopefully the play won't be too far removed from the original as he is a self confessed XCom fanatic.