I highly recommend the Beco carrier (www.becobabycarrier.com). It works for babies 7-45 lbs and can be used as a front pack or back pack. I take mine with me every time I leave the house with my 20 month old. It's very similar to the Ergo that other mamas here have recommended, the main differences being that it is cut a little bit trimmer in the seat, and it comes in brighter colors and patterns.
If you'd like to try one out, I also run Babies Bottoms and More in Farmers Branch, TX. (www.babiesbottomsandmore.com) We have several Becos in stock and you are more than welcome to come with your baby and try it out! Peppermint baby store has closed their brick and mortar location - I saw someone below posted a link to their website, just FYI.
You can email me at ____@____.com or call ###-###-####.
Good luck!
E.