I agree with John, if you do more regular instances, you'll get to know players on your server. If you have a good run and appreciate a players skill, tell them so and let them know you'll put them on your friends list for future runs. they will like that and probably reciprocate. I've lost count of the number of times I'll have someone I ran an instance with weeks back whisp me out of the blue asking me to join them. I have a large list of (non guild) players that i've instanced with now, and most of them are happy to do a run with me. This makes the transition to Heroics that much easier.

I tanked many many many pugs. A lot of the people I met along the way did the exact same thing John and Bono are describing. After a good run, one or more of the PUGs would whisper me saying they would add me to their friends list and I would do the same (especially if it was a healer). The more PUGs you do, the easier they become because you get to know sort of a good 'pugging network' - which I guess means you gradually transition from pugging to grouping with good non-guildies.