There's quite a buzz about using bumblebees as pollinators for greenhouse tomatoes - the trick is though that nectar (or substitute) has to be provided because tomatoes have none, and the bumblebees need both. Typical design has a sugar syrup provided in the artificlal bbee-nest.
I found this document by British beekeepers that lists plants rich in pollen, nectar, or both. I'd say it would be handy to have a nectar-rich (not pollen) plant handy to the tomato crop (pansies, for example), so the bumblebees have a source of energy to gather your tomato pollen without going further afield.
http://www.bbka.org.uk/files/library...1310045511.pdf