A great idea could really help a lot of ppl here. who's gonna work on it?
I already created it:
LockMyCoins.
Small explanation:
When you open the website an address will be generated for you (the private key can be copied, no worries). This will be the address used to lock your coins in a transactions, so you will need to send the coins you want to lock to that address.
After that the only thing you need to do is enter an Destination Address, how much you want to send to it (I advice you to send everything, haha) and when it should be accessible (you can enter something like "Tomorrow", "Next month", "23-11-2013" and many more options, just check that the Lock Time variable in the Json output isn't 0 / the output isn't empty).
The script will output an hex encoded transaction and a json one just for display purposes. You
have to save the hex one! After that go to the "Broadcast Transaction" and push the transaction. That will push the transaction into the network.
You push the transaction locking up the coins right away. The other transaction, the timelocked one, you don't need to broadcast at all until it becomes valid. There's no point broadcasting it, because it won't be stored or relayed. What you need to do is keep the timelocked transaction that pays the coins back out to you safe, and once it matures, you can broadcast it and it should be mined.
Michagogo, thanks for the last paragraph.