Where are you located? If you are in north/mid western MA or southern VT, southwestern NH go to yahoo groups to tradeperennials. I started a group because I got into to flowers, shrubs, herbs some years back & want everything! So I started this group & we have about 150 members. Folks meet individually & trade. New gardeners trade whatever they have - if not plants then something homemade, craft, recipe, manure, stones, bricks, mulch, canned goods, etc.
Also put a "wanted" on free cycle. Go to Yahool freecycle.org and it will come up with states then towns. There are many seasoned gardeners out there that are always thinning. Just make sure to look plants offered up on-line and/or get yourself a good perennial book because you want to know how it will spread, height, etc. Also go to your state site & search invasive plants to make sure you don't get & plant something that will take over.
As far as annuals there are many to grow from seed & some do re-seed themselves although some that re-seed colors break down. Join a gardening group on Yahoo & ask questions folks are happy to answer you. A local one is best - better if folks are in your area.
Many annuals as I said are nice my favorites are Zinnias which come in many colors & a bit different flower types. They are very easy to grow from seed and as long as you pick them they will go all summer. Also someone has just started a free cycle garden group that is like freecycle obviously but just for gardening. Or start a group in your area. Yahoo does promote it and you can make fliers & put up on boards. Then also people that are looking or offering flowers/plants send them a nice note with an invitation to check you group out. Also announce it on a regional site.