I like to live in shared houses.
When we were students, it was always some poor sod's responsibility to keep track of household bills, and share them out.
There can also be a sort of weird problem that people feel exploited if they're constantly the one buying the new soap and bog rolls, but these tiny amounts aren't worth the trouble or embarrassment of settling up. This tends to lead to shortages of milk, butter, soap, washing up liquid, dishwasher tablets, etc, etc, and makes it difficult to pay the cleaner.
I have solved these problems, by combining the power of Google and the wisdom of Luca Pacioli. We've used it for a year, and it works really well and is very flexible.
Here's a link to a blank Google spreadsheet for three people sharing a house:
Shared House Accounts for 3 (blank)
Here's an example where Alice Bob and Carol have been using it for a while, so you can see how it works.
Shared House Accounts (Simple)
And here's an example where Alice moves out, Dave moves in, they are all liable for various fractions of various bills, and they use the spreadsheet to remain friends throughout:
Shared House Accounts (Example)
Anissa, Rob, Sarah, Louise, and I used a spreadsheet like this throughout last year and it was great. When people moved in and out we knew exactly how much we owed them or they owed us and could see it was fair. Six months worth of accumulated debts were usually settled with a single bank transfer or handover of cash.
How to use it
Decide which one of you is the most numerate/computer literate (anyone with good O-level maths who has used google docs will do.) From now on I'm talking to them.
Make a copy of my blank spreadsheet, and change your names. If there are more than three of you, you'll need to extend it, which is easy 
Try adding some example bills, transfers etc, so you can see how it works. Use the examples as cribs.
Share the spreadsheet, with modify permissions, to everyone in the house. Then show them how to use it and tell them that it's not scary, and that you'll hold their hand when they need it.
 If anyone leaves a comment asking for blanks for four or five or six people then I'll make one specially for them.
Just let everyone buy things whenever they're needed, and add their own entries. Then you will always have soap.
Get whoever owes the most at any time to pay the next utility bill. That way you never get too far out of balance and you don't have to settle up between yourselves until someone leaves.
Set the spreadsheet to e-mail you whenever the others make changes so that you can tell they've done sane things that work. Occasionally arty types will put what appear to be random numbers in all the columns, but you can usually figure out what they meant and sort it out. There's a nice version control feature with Google docs, so even if someone really cocks it up you can just rewind and do what they meant to do instead of what they did do.
You can also use it for any sorts of payments, favours, expenses shared unequally, two people sharing the cost of something that's for all three of you., etc, etc.
There are formulae in the LIABILITY columns that share everything three ways.
If you want to make an entry that doesn't work like that, just replace the automatically generated numbers
with different numbers.
As long as you make sure that the PAID and LIABILITY numbers add up to the same thing for every entry, it will be fine.