Could it be Lemon Balm?

http://www.goldmountainherbfarm.com/PP/PPimages/lemon_balm.jpg

It looks rather on the mint side to me.

What is its scent? I agree that it looks minty, but the aroma should be a good clue.

Looks like the leaves have 3 leaflets and so not lemon balm.

Since it overwinters and it sounds as though you've had it a while, do you know if it blooms?

FataMorgana

What shape are the stems? If they're square then its a mint of some kind.

Not sure about that hellesbelles86. There are square stemmed plants which are not mints but I have never seen a mint with leaflets in 3s.

Most square stemmed plants are still related to mint I've learned but you're right about the leaflets- it is a little odd

I think it's Cedronella canariensis.

jaynine - that certainly looks very likely. And it's on Pearsons list too. Well done.

I grew Cedronella a few years ago & was lucky enough to have it bloom before frost. I had forgotten how pretty this plant is and how wonderful it smells: it's definitely on my 'to grow (again)' list for 2011.