I actually don't use Luxsci services as they are way too expensive for my tastes. I only mentioned them as they get nothing but rave reviews everywhere. I can't figure out why they don't set more competitive pricing for their services.
Zoho has a lot to like.
If I were gonna nit pick, the actual name, "Zoho" doesn't do much for me and the website is in my opinion, a little too busy, but other than that, they sure do have a lot to offer.
They have an enormous amount of features and options for a free provider.
I would guess that some paid providers don't offer as many services as Zoho.
I know I'm generalizing here, but you would have to actually sign up for an account to see all their different offerings.
I also mentioned them as the OP asked about services that aren't talked about a lot and I felt Zoho fit into that category.
Now, if the OP had asked which are the top three paid and free email services which don't get talked about a lot, that you personally use.
1. Fastmail - this is the only paid email service that I currently use. I have domains which require an annual payment and they are hosted with GoogleApps.
2. Polarismail: I was given a free account over at EMD but I believe those are gone and it's a paid service. Actually quite reasonable costs.
3. Eumx.net: Same exact deal as Polarismail and I think they're even cheaper.
1. Again, Zoho
I mostly use my Google Apps accounts but I will on occasion use all of the ones I just mentioned.
I'm really considering hosting a domain with Polarismail as this service looks quite promising and support is excellent for the costs involved.
Fastmail, I will probably drop at sometime in the future as I really don't like where they're going. Latest changes to the web interface were not to my liking.
Eumx.net is another excellent service. The few times I needed support it was quite fast and resolved the issue. Their website leaves a lot to be desired, but they offer four different interfaces. OWM, Horde, Squirrelmail and Roundcube. I don't know of any other service that does that.
They're a contender along with Polarismail as far as domain hosting goes.
It's pretty basic email, and you don't get a gazillion gigs of storage without paying for it, but the owner Mike is extremely well-versed in the email and web hosting business, very helpful, very friendly, and willing to whip up custom solutions if you ask nicely.