I bought a small 10L rucksack by OMM called the 'Last Drop' recently. seen plenty of others using them too.
Its great - got two large side pockets big enough for bottles and i can reach round to put them in/take them out without trouble. It can take a bladder too if you want, but i don't bother with them personally. Doesn't weigh anything either... Not quite sure if its what you're after, but i may well use it to replace my bumbag even on shorter runs. I think its really good and there's plenty of room for kit inside.