The mercury mitts are awesome but may be more then you need for summer use. They aren't light and don't pack that small. I use them for mid winter ski touring in Montana. I like how modular they are and will often carry the shell in my jacket and put it on over my fleece gloves when needed. I'll keep the insulated mit in my pack and wear it at stops if needed. The inner mit part is a lobster claw style wich some people don't like.
For fleece gloves my favorite material is Wind Pro (I have some rab and eddie bauer gloves made from it) which has a bit of a hardface treatment that makes the gloves wear better and offer a bit more protection from water and wind. These would also be my choice if i wanted something to bring for handeling an ice axe on a scramble in the summer.
They are sort of expensive and I also have some outdoor research pl 100 and backstop gloves (basically the pl 100 with a windproof material on the back of the hand) which are also good and a lot easier to find on sale but not quite as nice or hard wearing. The pl 300 is a great warmer fleece glove.
I find power stretch too thin unless you only use them inside another glove.
For more technical climbing or any situation where you are handling lots of wet snow/gear i'd want a glove with more water protection and a leather palm. I have some old bd punishers (a softshell glove) and guide gloves (a waterproof glove with removable liner) i use depending on how much warmth i want.
I also end up using kincos 1927kw lined work gloves a ton and they are really quite nice if you are on a budge.
Brand wise i'd check out Rab, Camp and Eddie Bauer First Ascent in addition to Black Diamond. Rab makes a really nice climbing oriented line, Camp makes some lighter options and eddie bauer has a few nice models that are often on sale. Outdoor Research also makes great stuff by they make so many models i can't keep them straight.
Having multiple pairs of liners is nice in wet conditions and use ample sno seal on leather (including the kincos).