I can help you come up with some of the best ideas for a romantic birthday that exist in today's world. You don't have to come up with spectacular ideas. Sometimes, the simpler ideas work best.

Buy a birthday card for the 30 days preceding your partner's birthday. Write something different each day and post the cards on the Fridge for the entire month.
Buy poster board and make an extra-large card. Fill it with pictures of the two of you together, happy and enjoying life. Include a little note that says
Hide the card in the closet, pantry, laundry room, in the car, or anywhere else that will surprise and delight your special someone.
If you have a large budget, why not rend a billboard located on the way to work? Say it loud and clear with really large font! Pretend to need a ride that day to make sure that he/she gets to see it (and you get to enjoy his/her reaction!)
Does your loved one have an iPod or some kind of MP3 player? Borrow it the day before his/her birthday and add lots of birthday songs like these:
Why not rent special birthday movies like "13 Going on 30" or even rent your partner's favorite movie, even if it's not birthday related... Relaxing on the couch can be a great birthday gift for some of us, especially if our lives are busy and we can't seem to find time to relax.
Hijack your partner's computer the night before and change the screen saver to a "homemade" birthday card. Tell him/her how much you love and care for him/her in the form of scrolling text on the screen. It can be a great distraction from work on his/her birthday!
At the end of the day, you (and you alone) know what's best for your special someone. But if you're still struggling with trying to find great ideas for a romantic birthday, here are some more ideas you can use: