Various ideas for knitting/crocheting/etc blankets, for babies or adults...
- Linda D Shoup's "Stashghan" - a blanket to use up your bits and pieces of stash yarn.
Biggest blanket for a given amount of yarn
Sometimes you only have a given amount of yarn, and you want to make the biggest blanket possible out of it.
If you knit it, then you'll need to decide how many stitches to cast on, and this can constrain the aspect ratio of the blanket. Err on the low side, knit it to the length required, and if you have any yarn left over you can pick up stitches along the edges later to make it wider. See also Modular Knitting.
Crochet can be done easily in all directions. Crochet a small square, don't fasten off the yarn, turn the square on its side and crochet along picking up stitches. Turn at the end of the row and keep crocheting in this direction until you have a rectangle twice the area of your original square. Turn the corner, crochet along the edge picking up stitches as necessary, turn at the end of the row and keep crocheting in this direction until your rectangle has turned back into a square. Repeat! The blanket will grow in both directions and you can decide when to stop because it will always be rectangular.
Make smaller squares until you run out of yarn and then sew or crochet them together.
Keeping up your interest on a large blanket
Change yarns often - see Marna's blanket.
Keep the same yarn but change stitch pattern every several rows. Pick the patterns carefully though.