Good field to study?

I have a strong interest in medicine and biology. I probably can't afford to go beyond a bachelor's degree in anything at this point, but I'm determined to at least go that far. Does anybody know what, within the general category of medical/biological stuff, would be a good thing to study to make it easier to get a job in the UK when the time comes to move? (A few years away still, but I'm patient and stubborn so it'll happen eventually)

Medicine, yes.  Just a Bachelor's in Science?  There are LOTS of very qualified Brits with those, so I don't think it'd help you to get a job.  Most lab researchers are beyond the bachelor's level, just as they are in the STates.  Studying nursing is a definite bonus, as is ultrasound tech, PET scan, nuclear medicine.

My niece in Florida is a cardiac and venous sonographer (ultra-sounds).  She makes buckets of money, and it took her just about a year of full time study and an exam.  It's a very interesting field, and sonographers are needed everywhere.

Cytology. Shortage in both the US and UK.

There are many careers which are accessible with just a bachelors:

biomedical scientist is the first that comes to mind, but check here for a comprehensive list of laboratory careers:

http://www.nhscareers.nhs.uk/careers/scientists/careers.html