Although it seems feminine, flowers are nice, I guess it would depend on his and your age. But in the least a card. My wife sends me flowers at times. Although I'm not thrilled with the flowers I see them as a symbol that I know she loves me.
So, at the moment my boyfriend is sick with a highly contagious eye infection therefore I cannot visit him. Tomorrow is our "anniversary" and we had plans to go out, but now we can't. Do you have any ideas on what to do to show my love for him?
Contact him and just tell him what you told us. You are sad you can't be together and look forward to when he gets better then you can celebrate as you intended.
As far as anything else, I'd wait until you actually see him.
Well, you could call him and talk to him on the phone and that would be nice or you could also send him an E-card with a Happy Anniversary on it. There's a site called www.123greetings.com that has a ton of E-cards and they're free also. A nice e-card and a phone call should do the trick until next year when you can be together.
Send him a nice letter, with some flowers and a picture if you.