Well, if you just want to blow some time and not really worry about losing money, take $20 and go play some nickel video poker. It’s gambling, but whenever I do it it’s mostly just because it’s something to do - most likely you’ll blow the whole $20 but you’ll be entertained for a few hours while you do it. Also, you get free drinks (alcoholic or otherwise).
Honestly, there’s a lot of stuff to do in Vegas, but I wouldn’t be caught dead there. I loathe Vegas. I think it’s the drivers. 
~Tasha
Go and gawk at the Bodies.
Seriously, it is amazing.
Former LV resident …
Try the indoor sky diving http://www.vegas.com/attractions/on_the_strip/flyaway.html
There are thousands of things to do like the above. They’re all a) novel, b) fun, c) a little more expensinve than you wish they were. Pick 10 and you’ll be busy for a weekend.
When I lived there I tried to do one per week & new ones popped up far faster than I could ever get through them.
The King Tut Exhibit at the Luxor. It really was an emotional experience for me. It was beautiful. Five bucks.
First of all, thanks Atrael for linking my site! And glad to hear it might help you somewhat Lemonbalm.
Sorry I am late to this party, but up to my eyeballs in final exams (I have gone back to teaching again) and doing websites for some new clients. Speaking of which, I have made a few minor changes to my site (got rid of the annoying confetti background and updated some info) but still have some major work to do to make it look better.
At any rate, as usual, the Dopers have all given you some really great advice.
As you are only going to be here for a day lay-over, I would suggest just taking a taxi to The Strip and taking a nice, long walk. Trust me when I say you will not be bored - just people watching, gawking inside a few of the new huge casinos…be sure to hit Bellagio and The Venetian, and maybe Paris and Wynn…nice design, some great artwork and detail, and those four properties alone cost them quite literally billions of dollars to build! You really don’t have to spend a penny to walk through and just let your jaw drop.
Let me know if you have any specific questions, but have a great time - and seriously, just go with the flow for a day…I promise you that you will not regret wandering The Strip and just taking in all in.