Opinions on a race memento please.

I've done a couple of races where the organisers give free photos as momento and think it's great, love having something truly personalised to show the kids what I've done and I guess in the future what I used to be able to do.... The set up was not a print it was downloads from the photographer's website of all the images taken - from a couple of places around the course.  Guess some people value having a photo record of their achievements.
If you have a medal, just make it a good one, I've seen some that are just a joke.  Really couldn't care about t-shirts.

why not give people options when they enter the race... medal, bottle of beer, ashtray, photo voucher, bootbag, T Shirt, Buff, cake, thermal drinking cup, whatever, etc...

People have different motivations - some people only keep medals from PBs or from marathons or ultras, others keep every medal and spend money getting them mounted in frames etc - we all run for different reasons so why not, given that you will need time to organise it, give people the option when they enter with say 1 month cut off to the choice option (after which you go with the majority to give you best leverage on price).  And nothing might also be an option which will save you money to spend on the other stuff so it should be better. 

I'd definitely go for running clothing - socks / hat / buff / gloves. Mugs are OK but only if they actually have the race name and preferably date on it - the last one I got just had the name of the running club that organised the race.  Medals I can take or leave. 

T-shirts have improved as generally now I do find you get a choice of sizes and more technical than cotton. BUT I hate the fact that they size them for men - so a small size is still always way too wide and long.  If there's the option to pay extra for one I wouldn't bother.

Beer and cake - absolutely