The usual thing is to buy a card and a nice present - underwear and chocolates are typical - and perhaps to go out for a meal (if you're thinking of this you should book early.) There is nothing wrong with any of this, but perhaps you're thinking of something a bit more unusual.

If you're able to spend some more money, how about a trip? This could be as simple as going to the cinema to see a film (romantic if that's what you both like) and a meal before or after; or to the theater if there is something suitable near you. Otherwise, you could consider something more extravagant like a special day out or even a romantic weekend break (as Valentine's Day is on a Tuesday this year, it may be hard to arrange something covering the day itself.) This page has several ideas for romantic destnations, and if you click the link '100 ways to treat your lover' you will find further ideas.

Have a great day!