The Family Fun website always has really neat ideas for all things holiday. If you are looking for ideas, here is a link to all their Valentine's Day ideas.
For Valentine Day's past, we have made the sweet shovel (we filled it with stickers, little raisin boxes and a couple chocolate kisses) and the sweet for the sweet - naturally for my oldest son's friends. Both were a huge success.
In addition to the card ideas, there are also a ton of fun recipes, games and party ideas.