Aaron and I started off our marriage establishing a monthly "allowance" for each of us, and it has been magical. No arguments over who spent what on what. No guilt over buying something for yourself. Here's how it works:
I never felt annoyed when Aaron bought something he valued that I didn't, and I never had to feel guilty buying what I wanted (as long as I had the fun funds saved, of course). At this stage in our lives, the monthly allotments are a little greater each month, but the principle still holds the same and works just as effectively.
We used to keep track of our funds on a piece of paper on our refrigerator. Now I keep track in an Excel file. You could also use Mint.com (just make sure to have the unused portion roll over) or a googledoc. Just find a system that works for you and keep track.
Do you use a similar system? Would this kind of thing be helpful for you? Start the discussion below in the comments!