It's almost always easier to avoid sewing, and there are tricks you can do with crocheting that help, and some tricks with knitting, but sometimes you just have to sew.
There's several sewing techniques illustrated here:
http://www.wonderful-things.com/newknit10.htm
There is grafting, a type of technique that imitates knitting, so you can't see the seam, which is done while the work is still on the needles.
http://www.wonderful-things.com/newknit10a.htm
Thanks for those links!
If I didn't have do seams, I would knit a lot more!