Formal:
* J'aimerais que tu sois ici. (This is the most literal translation and is very formal.)
* Je souhaiterais que tu sois ici. (Similar to the above, but a bit less formal.)
Informal:
* J'aimerais que tu sois là. (A more casual way to say it.)
* J'aurais aimé que tu sois là. (This implies that the person is not there and you are missing them.)
* Je te manque. (This literally means "I miss you" but can also convey the feeling of wishing someone was there.)
More poetic:
* Comme j'aimerais que tu sois ici. (This means "How I wish you were here.")
* Je rêve de te voir ici. (This means "I dream of seeing you here.")
The best way to choose the right phrase depends on who you are speaking to and the overall tone of the conversation.