Thought I'd share the pages I have bookmarked in my 5e books so far, it's a work in progress and I'd like to hear what pages you have marked so I can add them too :)

Players Handbook

Equipment (Weapons, armor etc.)page 143
Ability Checks - page 174
Movement/Environment (falling damage, light) page 183
Resting/downtime - page 186
Combat actions - page 192
Spell list - page 207

Dungeon masters guide

Dungeons - page 103 and 290
Between adventures (downtime activities) - page 125
Treasure (include random tables) - Page 133
Improvised damage and battle positions - Page 249 (Submitted by Valloncur)
Poison and Diseases - page 257
Injuries/shock - page 272

Monster Manual

No monsters marked yet

All pages are the start of a section that can be as little as 2 pages and as much as 20.

I'll add all the suggestions you guys make in edits so we've got a clear list for people to come and use!

<3
Zcotticus

EDIT: as requested, my system of bookmarking HERE