A fly that is tough to beat is an Elk Hair Caddis. I like to fish about a size 12 or 14. It's pretty much impossible to fish a fly like this incorrectly. You can fish it dead drift -or- swing it, skate it, twitch it, submerge it .....
If one presentation isn't working try another. I like to think of the fly as a marionette, using the long rod, I can animate it in a wide variety of presentations.
Here are some flies that we have had particular success fishing on a fixed line. Many fixed line fishers tend to simplify their fly boxes. Tenkara allows very precise placement and control, in many cases, that results in better success than relying on exact fly pattern imitation.
I was first shown this fly from Carl Richards, author of Selective Trout, Fly Fishing Strategy, and a number of other books. Carl said it was the best wet fly he had ever fished.
This fly is best tied and fished sparse, with about half the material shown in the picture. The fly has to be tied using mohair. I'm not sure what it is about mohair, but it does make a big difference.
The Chicago Leech looks a little bit like alot of things - nymphs,minnow, crayfish, etc. It appeals to a broad range of species - trout, steelhead, small mouth, large mouth, panfish, etc. It is also pretty hard to fish this fly wrong. It can be fished dead drift, stripped, swung, under a indicator, etc. On a given day, any retrieve may be effective.
When it comes to warm water fishing, I'm a big fan of foam. One of the best sources of foam I've found is flip flop sandals. These can usually be found for a dollar a pair, each pair supplies alot of bug tying foam. Not only is the flip flop foam cheap, it's easy, fast and fun with which to work. As an added plus, it is a very durable material, almost as tough as shoe leather.
Foam spiders are a great fly to use for panfish. Just cut out a rectangle of foam, round off the corners and attach to a hook-
Flip Flop foam poppers are fun to make and fish -
Then can quickly be turned using a drill or a dremel tool. Use a wooden tooth pick to attach the foam block to the dremel tool. Turn at a fairly slow speed using a small piece of sandpaper or an emery board to shape the foam.
Another generic, fishy looking fly. I originally saw a variant of this fly on Matt Zubweg's fine site/blog. It's a great search pattern when fished on the swing.