I know that a lot of these have been posted here, but I'm quite proud of mine, considering it is my first sewing project in AGES.
This is my t-shirt quilt, made from some of the dozens and dozens of t-shirts that I have collected from my time at Marshall University. Some of the t-shirts just have my school logo, others are shirts from more specialized events (the science fair I judge annually, my summer-research group, etc.) I also used blank squares, and I put some upside down because it is really meant to be a stadium blanket (for cold football games!), and I don't want it to matter which way it is held.
Front:

The back is polar fleece, which is Marshall fleece (!) that I found at the local Wal-Mart (yeah, I hate shopping there, but I needed Marshall fleece for my quilt!)

Sorry for the dumb look on my face, my boyfriend is not good at taking pictures!
**EDIT**
Ok, someone asked for a tutorial. I feel a little silly posting this because it was
that easy, but here it goes anyway:
1) Choose your shirts. I ended up using the backs of shirts as well (blank panels), but I would say that if you want a design on every square of your quilt, you will need about 25-30 shirts, if you don't mind having blank panels, about half of that. Notice that I also used a green bandana -- you aren't limited to t-shirts!!
2) Cut 13"x13" squares from each shirt. I made a template from cardboard first, which made it much easier (that way I didn't have to measure each square) **NOTE: the 13"x13" idea was taken from "Generation T: 108 ways to transform a t-shirt"...for all other parts of this project, I did not follow this project**
3) IMPORTANT! Lay all your squares out on the floor in the pattern you want them to be on your quilt. I don't suggest trusting yourself, because you will end up with two of the same shirt together or something if you don't do this step. It is hard to keep track of all the squares in your head.
4) Now, I sewed the whole top together in one evening, so I just took each row of squares, pinned and sewed them together and then layed it back down on the ground. After all the rows were sewed, I took the first two rows, pinned and sewed, then pinned the third, so on and so forth. I wouldn't recommend pinning the whole shebang together..that makes it very hard to sew.
5) Once you have everything sewed together, lay the top of your quilt out on the floor, right side facing up.
6) Note about fabric backing: If you are using a light weight fabric, use batting as well. I used fleece because I wanted this to be a throw, not a blanket, but since I made this, I made another one for a little girl's bed. I put flannel on the back and batting in between the layers...it is a perfect blanket for the bed!
7) I got two yards of fleece backing, which turned out to be perfect. Most fabrics are about 60" wide...allowing for seam allowance, you will notice that 5 squares (using 13"x13" squares) is just under 60"....this is not an accident. However, if you want your blanket to be wider, I would just get 4 yards and sew them together lenthwise, then you have ~120" to work with.

lay your fabric backing on top of your quilt top, right side down (if you are using batting, put the batting on top of the fabric backing) pin the two sides together, trimming any excess backing (and batting) as you go.
9) Sew the top and back together, leaving about a square's length unsewn to turn right side out. Use "invisible stitch" to close up your open square.
10) You can quilt this anyway you would like. I took the easy way out, and I just made a square knot using yarn and a big yarn needle at the corner of each square. I wouldn't suggest skipping this step, however, because you want the top of the quilt to be securely attached to the fabric batting.
VOILA!
This takes about two evenings. It is very easy to do all the cutting in one evening, and then all the sewing in the next...you could have a quilt by the end of the week!