2004 Litespeed Siena, 1996 Litespeed Obed, 1992 Miele (unknown model), 1982 Meile Uno LS.
You might need a new derailleur, but probably you'll just need to move it up a bit. Your main concern is going to be chainring to chainstay clearance. 48T is usually a pretty good big ring on a commuter mtb.
2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
First, does your crank have bolted on chainrings? Second, do you have any particular reason for wanting to stick with the same crankarms?
I ask those questions because chainrings are generally not very cheap. To replace all three chainrings, or even just the two largest rings, on a medium to low end crank will probably cost you as much as buying a whole new crank. If the bike is low end, you can get VERY cheap 48/38/28 cranksets which are great for commuting (in my opinion of course).
Do note that you may need a new bottom bracket depending on which crankset you go with. The above are all square taper so if you have a different interface and don't want to swap, you'll need to find something else. Your current front derailler should have no trouble with a 48 tooth big ring. If you wanted to go with a 50 or 52, then you might want to consider a road front derailler though that brings it's own set a of issues, and for that reason I'd recommend sticking with a 48. A 48/11 combo is bigger than a 52/12 (common road bike top gear) anyway.