I have 15-85 and 55-250, too. 15-85mm is a great lens for traveling. 55-250 is a super value lens yet delivers excellent pic quality.
The other 3 lenses I have are S50mmF1.4 and EF85mmF1.8 and Tamron17-50mmVC. All 3 lenses are great addition to my 550D and I am sure they will serve you well, too.
I am trying to find a Tamron28-75mmF2.8 in Taichung but no one stocks it..... >_<"
Listen to Candyz, Candyz oftens make appropriate suggestions to people to make sure no penny is wasted.