Just came across your post and I have to say I am actually pretty surprised noone has suggested this yet.....its the first thing that comes to mind for me when looking for non-spanking punishments.
I'm not sure where you live, so depending on those circumstances, the store and product might be completely differently named.
I read once about a cream sold at Walgreens stores (a drug store) called Capsaicin (used for arthritis pain). Supposedly its pretty darn potent and you have to be careful of how much you use and stear very clear of other close nether regions, as it would be VERY uncomfortable. I've heard once applied, it burns like a very well applied spanking and lasts a few hours. So much so, that the person applying must use gloves or thoroughly and quickly wash it off the hands before it sinks in.
I've been wanting to try it, and have seen it several times in my local Walgreens, but I'm afraid to ask my husband to buy it! Haha but just thought I've give my little input. Let me know if you try it!