A very good subject for a thread! Personally I think it's quite difficult to get this right and in some ways it almost always feel like a compromise, as it's easy to block too much sunlight from the bulb foliage at an earlier stage than what is healthy for the bulb. I also think it's necessary to balance the water needs of any companion plant, with the need of the bulb and this also can be difficult.
I use a lot of what is mentioned in the other thread, both annuals and perennials, but mostly perennials. Lately I have also been using lilies in an attempt to hide the emerging, narrow, but very tall foliage of the small spring flowering irises such as Katherine Hodgkins. I love these irises (unfortunately the deer also started to like them lately), but the foliage is problematic as it's so tall for such a small plant and it persists for a long time. This lily/iris combination seems good for hiding the foliage, time will tell if it will also be good for the long term survival of the bulbs! I mostly use OT lilies for this as they reproduce slowly and I think quicker reproducing lilies would smother the iris too quickly.
I also strongly believe that planting under bushes as you do and also planting under deciduous threes can be very beneficial as the ground there usually will be very dry during the summer. For instance last year I planted Cyclamen hederifolium below some European beeches and I hope that this will prove to be a better place than my old attempts of having them in borders, where they usually wont be long lived for me. Overall those difficult areas that nothing will grow during the summer as they are too dry or have too little sunlight, are places that I'd like to experiment with more for bulbs.
I however are a bit careful with using annuals to cover bulb foliage as the extra water needed (particularly at planting time, but also later) in my opinion makes it unsuitable for more sensitive bulbs. Drought tolerant annuals works best for me. Common cosmos works very well here and it's foliage is so finely divided that it doesn't block much light for the bulbs
I like snowdrops and Erythronium (dogs tooth lilies) together with plants that need to be kept moister during the summer. Their foliage disappears quickly and they also are tolerant to summer moisture, even preferring it. Also of course Daffodils would be good, but this is difficult here, because of the narcissus bulb fly.
Next year I'm planning to mix Geranium 'Rozanne' with spring bulbs as this plants habit, starting small and expanding a lot sideways during the season hopefully will work well.
