Kanger KR808D-1 is a fine model. The KR808D slim minis are the only real 3.7v minis.
Bloog and Smokeless Image and Halocigs G6 are the same kind of KR808D-1 threaded model - the new rubberized style
batteries, claiming slightly longer mah of charge, and finally a totally sealed end on the manual
batteries (and I doubt Kanger makes them since Kanger makes a different style). SmokelessImage Volt is the best priced I think. Only some of SmokelessImage's Volt colors are available as manual. The manual button is very small but they are nice. I only use manuals - I want by batteries to last their full life, not be killed by a carto leak. I also like that I have more control of my hit - easier to get a good hit.
Vapor4Life.com has the Kanger-style KR808D-1, non-rubberized, larger button on the manuals. I use their 2.5ohm WOW carto blanks. The threaded end of the current manuals have a decently closed off hole.