Well...what'd you have in mind to get? A new lens? Or a new body? Both?
If you feel that the body is not really limiting you (for example, you're missing a lot of shots because you can't increase the ISO, or it doesn't focus fast enough, etc), then concentrate on lenses. If you get EF mount lenses you can take them with you when you move bodies, potentially up to full-frame if you ever want to go that far.
In terms of lenses, it sounds like you need 1 pretty good general purpose lens, a decent telephoto, and maybe one wide or normal fast prime.
I'd kinda recommend the 24-105L f/4 IS USM as a general purpose lens, although the 24-70L f/2.8 is faster you won't lose as much at the long end. I see this replacing your 18-55, 28-135, and possibly the 50 f/1.8. You lose some at the wide end (you'd need to step back further to get everyone in an image) compared to the 18-55, but the image quality will be vastly superior. It is a bit expensive, at ~$1K new, but you can find it cheaper used or from people who bought it as a kit lens for 5d2/5d3 and don't want it. Alternatively, the new 18-135 could cover that whole range and be decent quality.
On second thought...the EF-S 17-55 f/2.8 IS USM is fast, and has good reviews as to it's image quality and is probably a more usable length for your family/inside shots. Something like the one of the 70-200 or 70-300 lenses would be good for telephoto. You don't need to get the most expensive version of any of those lenses.
For fast primes, depending on your needs, the 24L, 35L, 50 f/1.4, 85 f/1.8 are all viable options, and there are somewhat cheaper options of the 24 & 35 depending on your needs, and the 17-55 is probably as good or better at those ranges than the lower cost alternatives.
If you're wanting a new body, the T3i/T4i are good buys (buy without the kit lens if you can), or you can move up to the 60D or 7D (new firmware which adds a lot to the 7D). If you really want to spend, move up to the 5d2 or 5d3, but unless you really feel you will need those capabilities and are willing to start buying lots of L lenses, I don't recommend it for you yet.