It's our (sixth) anniversary today, and I'm awake at half-seven because I left a card out for my husband to find before he left for work, and he found it.
I ordered seeds of three very hot varieties of chillies and tucked the packets inside the card. Total spend: under £5, including the card.
Edited to add: last year's anniversary card was Domo Italiano, and I gave him a wooden pizza peel.