What are a good pair of double climbing boots and crampons?

The guides will typically recommend double plastic boots on Rainier, primarily because they are warmer and easier to keep dry on overnights, but I don't know of any plastics that are semi-automatic (heel bail/ toe strap) like you mentioned.

Depending on whether or not you get cold feet, I would honestly avoid the double plastics altogether. Unless you are doing high altitude climbs like Denali or extremely cold overnights (consistently below zero), they are not necessary. I owned a pair of good double boots before but sold them. They are heavy, bulky, and difficult to move in. Spend the money on a good pair of leather mountaineering boots, (this is what all the guides wear anyway). Good brands are La Sportiva, Scarpa, Asolo, Mammut, and others. Probably the most popular model out there is the La Sportiva Nepal Evo. Both my friend and I own a pair of these and they are unbelievably comfortable and versatile. I use them for ice climbing, cool weather hiking, glacier travel, and winter mountaineering. The only downsides to getting a leather boot are that they do not have a removable inner boot and can be more difficult to dry if they get wet, and they are not as warm as bigger double plastic boots. If you really want a good boot, there are some double leather boots, but they are QUITE expensive (La Sportiva Spantik $699).

Honestly though, something like the Nepal Evos (you can find them for 350 to 400) would be absolutely fine for Rainier. As for crampons, assuming that you aren't going to be doing any ice climbing with them, I would go with the Black Diamond Sabretooth or Petzl Vasak crampons. I have used each and they are both good versatile crampons for the price. They are both available in full and semi-auto versions.

Is this for summer? I will give advice assuming it is, winter would be much more hardcore...

Well I don't know much about Rainier, but it's only 4300m and on a roughly similar latitude to the European Alps, so I'm assuming it's roughly Similar conditions to Mont Blanc.

If that IS the case, and forgive me if I'm wrong here, double boots are ridiculous overkill. I do Mont Blanc and the surrounding peaks in B2 boots, which are mountain boots, but not winter mountain boots, and certainly not high-altitude boots like you usually use doubles for. I use the Scarpa Manta, if you'd care to look that up, £190. These are only suitable for C2 crampons - that is, ones with a heel bail and toe strap, whereas all doubles are high-altitude mountain boots and so come with heel and toe bails.

These are extremely comfortable, so much so that I was wearing them a lot around town and to/from work recently when we got quite a lot (well, less than a foot) of snow here in London. I even wore them on the London Underground, and didn't feel too hot or look ridiculous. The same could not be said for double boots.

However, if you are sure you want something more heavy duty than what I use, I'd go with the previous answerer's recommendation of La Sportiva Evos. LS are a very well respected make, and make a range of boots over what you're looking at, so check them out.

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