Well, I am just like you and bought 550D with 18-55is kit for my first DSLR in April 2010.
Although I am not an expert in taking pictures but for sure i have tons of fun with my 550D. So, you can start from there and trust yourself, you can't go wrong with 550D.
I took a lot of pictures of my twin sons and family members, my photo file number is near 10K and getting close to 10k. So, although i am not an expert but for sure i can tell you how to have fun with your next new 550D.
A few additional lenses are needed to complete your fun package.
The first lense I bought in addition to my 550d is: Canon 15-85mm IS USM
Pros: super sharp at all focal length and color is awesome for face pictures if you have good light environment. Can't believe how nice it is to my 550D, the photos shot with this lense are keepers.
cons: not a fast lense to capture my twin sons in livingroom..... even with all my lights on in the living room. P.S. I don't have 580ex or 430ex.....
The second lense for my lovely twins: Canon 50mm f1.8 MK II
Pros: Super value for the money and no other lense at this price can beat this cute little fella. Picture is sharp, shutter speed is good indoors and it can capture my twin son's actions. Great for taking it out and even if i lost it i won't feel a bit sorry. This is just a super cheap lense with great perfromance. Some people even say it is sharper than Canon 50mm f1.2L. I have never seen f1.2L but I certainly have lots of fun when i bought this lense.
Cons: cheap looking lense and all plastic sound. Loud focus and focus slow.... still, I like this lense.
The third lense for my 550d: Tamron 17-50mm Di II VC (b005)
Pros: Big apparture at 2.8 is so nice to use indoors. VC works better than i thought it would be. Solid build lense and you do feel the quality of the material. Picture quality is good even without VC turned on. Works fine with my 550D in AV mode. I use AV mode when B005 is mounted on my 550d.
Cons: VC vibrates when operated. 10% of my photos turned out to be too bright or yellowish. Focus speed is significantly slower than A16 or my C1585ISUSM. I would say B005 focus speed is pretty much like my 18-55mm IS. VC works loudly, you can hear it very clearly indoors. Does not work well for my 550D in AV mode.
Generally speaking: super cheap thrid party lense with big f2.8 apparture. VC is a nice addition but not really needed and VC's noise is loud.
The fourth lense I bought for my twin sons on 550D: Sigma 50mm f1.4 EX DG HSM
Pros: CLASSIC piece of art in 50mm. Performance by looking and it sure feels authority in hand. Picture is super sharp at 1.8 or 2.0 in my case. Color is mono tone refelects true world color condition. Feel condfident taking pictures of people or landscape knowing I will get pretty good results from this lense.
Cons: paint job on lense is lousy, not easy to clean and looks like rusty.... Generally they are not focused right from the retailers, you have to take it to the SIGMA and boy they do make your sigma perfrom god-like. hahaha. Great people and great service I got from SIGMA Taichung.
For your information: I live in Taichung and i don't care if this lense focuses precisely since i can always take any sigma lense to Sigma Taiwan Ltd. in Taichung to have the lense serviced free. I took this lense to them right after bought the lese from the retailer and their engineer is polite and most importantly of all, they fine-tuned the lense for me in less then 18 minutes right on the spot. Hahaha, can't really complaint with that kind of speed and service you get is better than my lexus experience.
In sum, please do have fun with your next 550D. Buy your lenses one by one. I have lots of fun with all my lenses except the junky 18-55mm IS. Ever since I bought 550D as my first DSLR, we have more laugh in the family. We talk a lot more about fun times when pictures are shown to my family members. Especially my parents, then enjoy looking at my twin son's photos and share all the happy momories within family member.
Most of my finished photos are lousy and amature. However, 550D and my lenses certainly have served me well by capturing the right moment for our memory.