Edinburgh -- Salad??
I would never profess to being a salad expert since I don't eat it that regularly however I would say that this is something that you really don't want to get from the majority of pubs/cafes as it's more likely to be bland and limp!
I'd sugest that Deli's tend to be your better option with some specific cafe's. I think that all of the following places have web sites so if you google them you should get a feeling for their menu's etc.
Henderson's (probably the original Edinburgh Vegi cafe, it's been around for years)
The Story Telling Cafe
At a guess, maybe Urban Angel although I've not paid any attention to the salad options when there.
AWaiting has covered the best two options IMO -
Urban Angel - the one on Forth Street - always has 5 or 6 salad options available that change every day - you can ask for a selection of them on one big plate. great quality, really fresh, nice and light and quite inventive flavour matches. pretty cheap as well, especially if you get a take-out box - can feed 2 people for under £4. they also do delicious smoothies and great cakes that you will see on the counter as you walk in.
then just around the corner is Broughton Street Deli - my favourite - bit more rustic than urban angel perhaps, but some of the salad and veggie options here are delicious. If you like Ottolenghi style salads go here - they basically copy half their stuff. Again the best option is to go for a mixed plate of all the different salads. One thing I would beware here is the pricing - it always ends up costing a fair bit more than the advertised prices, which leaves a sour taste in the mouth. it's quite underhand, imo. however i keep going back for the delicious food. best thing ive had there is there roasted eggplant and pomegranite slathered in yoghurt, and the veggie lasagne.
elsewhere leo's beanery in stockbridge tends to be decent-ish food with salad options.
Being pretty chilly I don't think Edinburgh is well known for its salads but I would try either urban angel ( I prefer the forth street branch) As johnnypd suggested or Leo's beanery also. Urban angel is antipodean in style and slightly more restaurant-y than Leo's beanery which is more of a cafe and does fantastic home baking and a smaller but very fresh menu. The dovecote gallery cafe also does an excellent falafel salad and great coffee too.