Doug Braun, of Tucson, AZ, recommends the "Garden Song" 10 ounce feeder from Opus, Inc. Here is Doug's review:
Here in Tucson we have a variety of hummers year round and I have gone through four different feeders since my wife and I moved here two years ago. Basically, the main problem we had was (Gila) Woodpeckers and other birds hanging from or standing on the feeder trying to get the nectar. I wouldn't have minded this so much, but the feeder hangs over our apartment patio and all the (non-humming) birds were creating quite a mess (if you know what I mean). The Garden Song feeder is egg-shaped with two small openings near the bottom and has no protuding parts or "base" for other birds to grab onto or stand on (there is one exception mentioned below). The small size is convenient, since it is necessary to change nectar often in the heat of the desert here anyway. The feeder is easy to clean with a special brush (bent at 90 degrees) purchased at a wild bird store (same place we got the feeder). We have had this feeder for several months and can recommend it highly (I have no affiliation with the makers of this feeder).
Oh, yes, the exception. It appears that small house wrens can hang (with one foot!) from the feeder openings and get the nectar. It is quite a sight and we don't mind since they don't make much of a mess.