Rachel,
I had a Garmin 305, broke it (dropped my bag on a solid surface and screen cracked - very frustrating).
Eventually replaced it with a 405.
Overall, i preferred the 305, but both have pro's and Cons:
1 305 pro's... 4 displays at one time, better control due to all "button" control, price.
2 305 cons... tends to be bulkier, takes longer to pick up signal, battery life.
3 405 pro's.. looks good, is lighter, can be used as a watch, battery life.
4 405 con's.. bezel sometimes takes a life of its own - i tend to lock it now particularly if its wet, harder to control on the run, 3 displays only, price.
Whichever you choose, your'e better off online i feel as you'll get a better deal. Garmin will look after you it there's a product fault, whereas if like me it got broken due to stupidity they wont!!