Judging from the shape of the pronotum, I would say it is a spider wasp (Pompilidae). I realise that some of these characters aren't always that easy to recognise and see.
Note that there are some pictorial keys to many of the insect families at
http://anic.ento.csiro.au/insectfamilies/
This is for Australia, but the major groups are found everywhere.
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