I can recommend a few by lowepro:
slingshot 100
- great little bag to hold DSLR and a couple of small lenses in lower section and a sarnie or two in the top. Bag "swings" round on one strap and you raise the DSLR out of a side pocket. Bag stays in place to use as a mini platform for lens caps and for resting things while you change lenses
Fastpack 200 or 250
- larger bag for carrying DSLR and four lenses plus a sarnie and change of clothes in the top. Also has a slide-in section for a laptop. Very good as a weekend/overnight bag or for travelling.
Both can be had pretty cheap on amazon, but it's worth having a search for each on google and youtube - lots of people do video reviews and gives you a chance to see them in the flesh and the amount they can hold:
slingshot
fastpack
For your position I'd recommend the fastpack; don't buy a bag that will hold your kit, buy a bag that will hold a little more - you may nto intend to buy anymore lenses, but in 6 months time you will have!