Forgotten heavy bands from late 60's to early 70's


Have been a fan of hard rock/metal since high school. Always liked the heavy/physcadelic bands equally to the metal bands I grew up with Ozzy-Maiden and Scorpions ect. Recently on Youtube I discovered some heavy/physcadelic bands I was unaware of. 13th Floor Elevators-Five Day Rain-Probe Direction-The Hook and Vahalla. Are these bands albums worth persuing? Feel free to mention any other band that deserves to be heard. Look forward to your responses.
dayglow

Medicine Head, they released their Dark Side of the Moon album just before Floyd and nearly caused Floyd to change the name.

@lordmelton - it might be Greenslade, but Roger did SO many album covers back then, who knows what I was thinking of? 

That Medicine Head one - wow, that's a real obscuro!!