In reply to Tom Ripley Mountain Guide:
I tend to remember the general experience and scene rather than the route, so here's my list (with the odd example).
1) On a weird move, usually bouldering but not always, short-term muscle memory improvements from no-chance to success, within 5 tries, never get it first time on any visit (there's one at Ramshaw, but it isn't in any guidebook).
2) Cragging in the sun in the middle of winter without pain and discomfort (like today at Beeston).
3) Training for a sports move all winter, then doing it a totally different way when you get to the crag (e.g. Finger of Fate at Buoux). This is a trivial one, but somehow sticks in the memory because it's really about getting better.
4) Multi-pitch Alpine rock. Doesn't matter if it's bolted or not (Motorhead, Septumania, Boulder Highway, Kalypso, Kingspitze E Face: pick one it doesn't matter which. Face stuff though, not Salbitjen or Cham ridges).
5) Sea cliffs in the UK - especially Gogarth, parts of Pembroke like Mother Carey's, parts of Cornwall like Chair Ladder, Parts of Devon like Culm and Lundy, and sea stacks. The more pitches the better. (Helluva Slab stands out as a nice solo, but that's just a weird memory)
6) Surviving a few 40-footers totally unhurt (important to get this done when you're young).
7) Alpine 4000m peaks on skis (ditto, before it becomes hard work).
8) New routing, easy or hard, on-sight or after practice; all good stuff, and you get to name this shit.
9) Climbing in weird places like deserts (Utah, Wadi Rum, Hoggar) that you might not otherwise go to.
10) Having something and somewhere to aim for on the next day out (Lakes) or trip (Croatia) - and the guidebook to, well, guide you - just enough but not too much.
The appeal of bouldering is encapsulated in (1), sport cragging comes under (2 and 3), improving under (3 and 6); the rest are (ahem, pretentious I know) landscapes of the mind - what makes climbing different from football.