I’m going to buy some filters for my camera, 40D, with a 72mm 28-135 zoom. What brands should I look at and what should I stay away from? I know I want a polarizing filter, I shoot a lot outside, but I shoot in almost all conditions too; so what else should I look at? I do sports, landscape, animals, people, both inside and out, astronomy, cars, art and anything creative. Also, what brand of close-up lens is good (the kind you screw on and stack), as well as what is a good size lens to get for close-up work? 10-20mm-ish?
Thanks,
Jaybird

Stay away from cheap filters !
The best are multi-coated to minimise reflections between the lens and the filter.

I don't think any kind of screw on closeup lens is as good as extension tubes.

I don't use any other filters, though for astronomy you may want Sodium line filters if you're close enough to town to get an orange sky glow interfering with your images.

By far the filters I use the most are my graduated neutral density filters.

If you want quality close-ups get a macro lens, not an adapter.