Sometimes when caught I'll just stare blankly at her as she's talking to me...after a few minutes of that I'll ask her if she'd rather me go back to hanging out in the bars...
I've also found that having "his and hers" credit cards work out pretty good. I have mine for "play" and she has hers for "whatever" and we keep it separated...I have an old Capital One card that has a fairly low balance. I don't have statments sent to the house and if I need something big I get it shipped to my office. I get most of my computer stuff that way...She has no idea that I just replaced the graphics card with a new one. For her reading mail or simple surfing looks just the same but if I can go from 21 FPS on Call of Duty 4 to 64 FPS it is money well spent!!
If all else fails I simply try the old standby..."I've had that sitting around FOREVER!!! Don't you remember we already talked about it???"
I sleep on the couch occasionally...
The existence of flamethrowers is proof that someone, somewhere, said to himself, "I want to set those people over there on fire, but I don't feel like walking over there to do it."