The Shimano Sora is always a good choice. They are inexpensive, made very well, and are pretty light considering the price. I have used them on 5,6,7 and 9 speed cassettes. I have used Sram Gripshift, Shimano Rapidfire, and my favorite, cheapo friction shifter. If you are looking for a long cage, i would recommend the Shimano Deore. Both the Sora and the Deore share much of the same research and development as desplayed in some of their high-end components. The Sora weighs the same as the Tiagra, as does the Deore weigh almost the same as the XT. Much of the moving parts are the same too. If you are not shifting constantly (were doing trials here, not XC) then the integrity is much the same. I have broken an XT short cage just as quick as a Sora, yet the XT is three times as much. With most derailleurs you will be paying for smoother pulleys, and smoother shifting. Using good housing, proper cutting and machining of ferrules, and using a teflon-coated cable can help just as much with shifting. Good luck!