There are so many great umbellifers (I love them beyond reason)...but yep, a,gigas won't do much this year...and then it dies after flowering. I have yet to find a really good perennial angelica since most seem to be monocarpic (apart from a,arguta)...but this is not the case for cenolophium denudata, sesili gummiferum, selinum wallichianum, chaerophyllum roseum, pimpinella, molopopspermum (sp?). Why not just sow some quick annuals such as orlaya, ammi, daucus carrota (which you can get with dark foliage)...giant fennel or even parsnips. I also grow the giant melanoselinum decipiens.
I think I have already mentioned my favourite euphorbia...if you can get your hands on e.ceratocarpa, I think you will love this 5 ft, high and wide, effortless, endlessly blooming and absolutely glorious spurge,
gentlegreen. Far better than the usual e,characias wulfenii. Mine grows between a very floriferous pink rose (Madame Gregoire Staechelin) and is looking glorious at the moment
O, another plant you might like - the giant thalictrums such as t.rochebruneanum 'Elin' or the really spectacular t.delavayii 'Splendide'.