@Stoo is the resident expert on Toby wrecks and areas to dive since he has a cottage in Toby (which he refers to on FB as Squalor Holler).
Whaddaya want?
Ya, I more or less live in Tobermory in the summer....
That pic is at an area known as the Grotto... Very touristy in the summer but still a cool place to dive. Boat access only unless you're (a) 20 and (b) dumb. Don't ask me how I know...
Regarding some of the other questions here...
Yes, DD is the only shop in town. They're busy and operate up to eight boats. I don't think it's fair to characterize them as a "cattle boat" operation. The max they can take on any of their boats is 12 I think, but I see them leaving daily with 4, 6 or 8 divers, especially during the week. Walk-ons are generally "majority decides", subject to weather etc.
We do have lots of wrecks here, but it's the water and topside scenery too. Think total package. There's also some great, more technical diving, an hour down the road. Logistics there are more complicated. Contact Fully Tec Charters for their trips to Manasoo and Jones.
Personally, I think the best conditions are found late spring. It's cold (39 - 42 typically) but vis can be upwards of 100' easily. Basically just like the Caribbean minus the warmth. Summer is warmer up top, but town becomes very busy. Fall is awesome diving, but the wind starts to blow about Sept 5 and doesn't stop until May. Boats stop running after our Thanksgiving, which is early October.
If you are coming up and need accommodation, it's not too early to book for summer now. Lot's of hotels/motels/cabins/camping and private rentals (like my place!)
There are many images of the area on my website (in my signature... )
Feel free to post questions here, or DM me!