Greenhouse crops like tomatoes, cucumbers, peppers etc - go for it.
Use seed trays with propogator lids, sow in cells but only use
two-thirds of each cell pack. If it looks like a cold night, put a
lidded jar of hot water in the spare third to keep the seeds warm.
Alternatively, cover them with fleece or bubblewrap while the heat of
the day is still there.

Most veg seeds can be planted striaght outside anyway - things like
carrots won't like being moved.

Have a look at this website - I've found it invaluable.

http://www.powen.freeserve.co.uk/

Good luck!