A few years ago I "re-learned" to knit, mostly from this site, and embarked on a project to make afghans for each member of my immediate family. Altogether I made 9 afghans, some for family and a couple for gifts. Two were crochet and the rest were knit in various patterns. All were well loved and are well-used by the recipients.
My two favorite yarns for afghans are Lion Brand Homespun which makes an incredibly warm and cozy blanket when done in a tight weave. I made one for a cousin and one for myself, just using single strand, and we both consider them "magic blankets". You cuddle under one of these and just get SO comfortable! I always doze off for awhile! The colors are kind of tweedy or heathery and it's a boucle-type yarn so the strand is twisty. But once you get accustomed to working with it it's super. (I also made one for my husband out of Lion Brand Chenille. It's very warm and the colors available were nice).
The other yarn I used a lot is Caron's "Simply Soft" for several of the afghans. It's lovely yarn. Thinner than you might think but with a lovely sheen, super soft and surprisingly warm.
Both yarns are synthetic and easily machine washable and dryable on low heat.
I got some lovely patterns out of the two Herrschner's Blue Ribbon Afghan books and would recommend them for inspiration. They're quite wonderful!
Hope this helps. The afghans I made were certainly a big hit and I wish you all the best in your blanket-making!