What I do is keep a running record of items I want from (wherever). Sometimes it's a list with my garden records, but what's worked best for me is to make a seed sources folder in my bookmarks, and within that make a folder for any seed source that has things I want.
Sand Hill, Victory, heirloomseeds.com, Baker Creek, Pinetree and several others that I order from only occasionally, or haven't ordered from yet, but probably will at some point -- Nourse Farms has joined that group as a result of this thread . . . and I do include Burpee and Parks. I find saved lists for those two especially useful when I occasionally run across a really good discount offer -- I know right away what I want that I can only get from them. I would have had Miller Nurseries on the list but since they were merged with Stark . . . don't know.
When I am browsing a source and see an item I want, or run out of something I use, I save a link to that item in that source's bookmark folder. In fall or early spring, when I order seeds, I browse through the source folders, see which sources have items I *really* want, and then see which of them can best supply whatever else I want. So most years I place orders from two or three sources, not necessarily the same ones from year to year.
This year I ordered from Sand Hill and Victory, and had a couple of other orders planned, but have almost decided that I may place another order from Victory as they have a couple of things I want and can't get elsewhere that I missed on the earlier order, so I may just fill in another Victory order with my remaining "get about anywhere" items.
Or I may decide that most seeds keep pretty well here and place two or three more orders from various sources
