Bitcoin client which doesn't use wallet.dat? Is it possible to use Bitcoin client without wallet.dat file, by entering your addresses and being able to see the balance, but without the ability to spend bitcoins? I know that it's possible to backup wallet.dat and use another wallet.dat, but in that way you don't see your transactions and balance and can't label your addresses etc.

If it's not possible in official client (I believe it isn't), are there alternate clients that allow this? The point is to be able to backup wallet.dat and plug it in only when spending bitcoins, but not lose the ability to see your transactions in the meantime.
This is not exactly what you're asking for, but might be helpful. Bitcoin v0.4 supports encrypting wallet.dat, so you cannot spend without entering the password. Basically you would do something like:


make a copy of wallet.dat
encrypt your copy with Bitcoin client v0.4 and set a long random password (one you will easily forget)


Voila, you have just created your read-only wallet. Because of 100 keypool you will even see some new transactions made with original unencrypted wallet.dat

You can download Bitcoin v0.4rc2 here.