I travel a lot and am looking for a fast muscle building/maintaining workout that I can do from anywhere.

My goal is not to become "ripped", it is to maintain decent muscle tone and avoid becoming fat while continuing to drink good beer, eat chocolate cake / fries with bacon & cheese, etc.... all while aging. Even at rest, muscle burns more calories than fat. My strategy has always been to maintain enough muscle that I can eat all sorts of tasty food and still be in negative/neutral calorie territory. I run and do other things that burn calories, but this is for fun not fitness.

I am looking for a set of exercises with the following characteristics:
1) Require no equipment -- things that I can do in a hotel room, if necessary
2) Are fast -- Difficult exercises that strain my muscles quickly so that I don't have to spend much time on them
3) Work useful/visible areas that make me more attractive -- a nice chest and abs attract positive attention. A strong core is good for general fitness.

My standard workout is 3x30 push ups with advancement occurring by reducing the break time between sets. Done daily, this has kept the flab off for years.

I'm looking for exercises to add. I've tried leg lifts (lay flat, raise straight legs to 90 degrees) but I need 50 of these before I feel anything. I get bored before I get strained.

Bench crunches look promising (3x30), but I think that I need something more. Any recommendations?

(Pull-ups are out. If I break a hotel doorframe, I pay whatever fee they think is appropriate.)