One word of caution regarding sexercise... if she's able to concentrate well enough to keep count, then the two of you are not doing it right.
Seriously I think most of the suggestions are good (well, the Wii Fit, get it if you want to, for fun, but honestly there are far more efficient / less expensive ways of getting your exercise on).
Sustainability is the key. If you're going to spend money, spend it on things that will encourage you to be consistent and exercise several days a week, every week. You don't even need to spend money for that -- get friends or loved ones to hold you accountable, make a chart to publicly check off each day, etc.
One that I'll add...
Get a pedometer. This isn't indoors, obviously, but it will allow you to track how many steps you take per day. A Nikeplus kit is great, but a pedometer is more than fine and costs only a few dollars. The point of having one is that, once you know you walk, say, 2500 steps / day, by doing several little things like the ones mentioned above -- taking the stairs, parking in the back of the lot, walking around the block, etc, you can easily add 15-20% additional walking per day -- you could be at say 3000 steps/day instead and it will burn some extra calories and have a mild aerobic fitness benefit with little effort, and it will be sustainable.
As you walk more, too, you can use interval training to get yourself able to run short distances, if you can't run now -- e.g. walk 1-2 miles with some 50m runs interspersed in it. This is great cardiovascular training and also provides you a metabolic boost.
I think the suggestion to keep it simple is great. It's way to easy to invest heavily in gear that will end up in your closet, and fail in a year's time to have improved your fitness. Concentrate instead on anything that makes you exercise more often and will keep you going rather than getting burnt out.
