I use 550D, too. I do portrait shots only and maybe I can offer you some of my portrait lens experience. Just to let you know, my portraits are all shot without flash.
1. Sigma 50mm f1.4 --> THIS IS MY ALL TIME FAVORITE INDOORS - great for indoors especially where lights are not enough - Excellent outdoor too with amazing bokeh - Sharp and HSM works well in my opinion - many professional wedding photographers choose to use this lens
2. EF 85mm f1.8 USM - Incredible bokeh - sense of compression is amazing - very sharp at wide oper aperture of f1.8 - good for head to shoulder shots indoor - great for outdoor portraits for half-body or full body portraits - many professional wedding photographers choose to use this lens
3. Tamron 28-75mm f2.8 A09 --> THIS IS MY FULL TIME FAVORITE OUTDOORS - worldly renowned portrait lens on both FF and APSC bodies - great center sharpness and amazing bokeh - F2.8 is workable aperture size - flexible focal length makes it my no.1 choice of both indoor and outdoor portrait lens
4. Tamron 70-300mm f-5.6 VC USD - great compression at center which produces excellent head shots at and over 135mm focal length - amazing sharpness that is comparable to prime lens at long focal length - bokeh is a totally diferent experience with other of my prime lenses - VC works amazingly and is better than average IS and is better than my B005 - versitile focal length makes it not only a good tele lens but also a great portrait lens.
I would love to have EF 70-200mm F2.8 IS USM II but this lens is just to expensive for me and if you really love portrait photography, please do search this lens on flickr for portrait photos.
It is always nice to see people are interested in portrait photography. However, please also be advised that no sigle lens or photo is more valuable than spending time with your family and loved ones. It is the journey you be with them that is valuable. Please do more portraits of your family and share the photos with them, you wil find yourself in a happy position within your family.