Would definately like to go to one of the RHS flower shows this year: RHS Tickets
Would also really like to visit the Eden Project this year.NGS Open Garden's scheme is such a good idea too - you can visit a multiude of lovely gardens and donate a small amount to charity as you do.
National Trust Gardens are more often than not gorgeous too
Barnsdale Gardens looks like another lovely place to visit:
I will post more ideas as I find them.....