Theres a good sticky thread at the top of the blending forum with general info on blending templates. Theres a similar one on the Sweet Marias website which could be a good starting point.
They both follow the general rule of combining base beans (ie. bigger bodied, sweet, clean beans like Brazil, Colombia, India, Peru) with various other types (eg. acid beans like lighter roasted Africans and some Central Americans; low beans like monsooned Malabar, most Indonesians, darker roasted Africans; fruit beans like Harrar, dry-processed Sidamos, some Central Americans; etc...).
That can be a helpful way to think about it - essentially asking yourself what elements you want in a blend, and combining beans so as to achieve it. Of course, its never that simple, because the beans interact in unexpected ways.
One of the most interesting experiments we ever tried was to get 4 different beans (in our case Brazil, Panama, Ethiopian Limu [wet-processed], and Ethiopian Harrar [dry-processed]) that had been roasted in the last 3-4 days, then cup them all as single origins. We looked at our notes and made guesses about what flavour elements would go well together, then each came up with a blend. The three of us then cupped these blends and chose a winner. In the end, we had 50% Brazil, 25% Panama, 15% Harrar and 10% Limu.
[interesting thing we noticed was that the lightly roasted Limu (very acidic) really highlighted the fruitiness of the Harrar - we loved the fruit so most of us added 25%+ Harrar into the blend, but it worked a lot better when it was kept fairly low but highlighted and sharpened by the acidic Limu. This was one of those unexpected interactions I mentioned.]
Anyway, the actual blend we came up with isnt the point. The point is that by cupping the beans to see what characteristics they might bring to a blend, then re-cupping the blends to see whether our predictions were correct, we learned a great deal about the process. It was also fun!
Rather than giving you actual blend suggestions, Id recommend you do a cupping thingo like this.